diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 22bb4f4..671fb9e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -3,15 +3,42 @@ on:
     branches:
       - master
   pull_request:
+
 name: CI
 jobs:
   test:
     name: Test
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        go-version: ['1.17', '1.18', '1.19', '1.20', '1.21', 'stable']
     steps:
-      - name: Checkout code
+      - name: Checkout Repository
         uses: actions/checkout@v4
+
+      - name: Setup Golang Environment
+        uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go-version }}
+
       - name: Init Hermit
         run: ./bin/hermit env -r >> $GITHUB_ENV
+
       - name: Test
-        run: go test ./...
+        run: go test ./... -race -shuffle=on -v
+
+  lint:
+    name: Go Lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - name: Setup Golang Environment
+        uses: actions/setup-go@v5
+        with:
+          go-version: stable
+
+      - name: Lint Go
+        uses: golangci/golangci-lint-action@v6
diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 0000000..fa89471
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,56 @@
+linters-settings:
+  misspell:
+    locale: US
+  govet:
+    enable-all: true
+linters:
+  enable:
+    - asasalint
+    - asciicheck
+    - bidichk
+    - contextcheck
+    - dupword
+    - durationcheck
+    - errchkjson
+    - errname
+    - exportloopref
+    - fatcontext
+    - gocheckcompilerdirectives
+    - gochecksumtype
+    - gocritic
+    - godot
+    - gofmt
+    - gofumpt
+    - goimports
+    - gosec
+    - gosimple
+    - gosmopolitan
+    - govet
+    - ineffassign
+    - makezero
+    - misspell
+    - musttag
+    - nilerr
+    - noctx
+    - nolintlint
+    - paralleltest
+    - prealloc
+    - predeclared
+    - reassign
+    - staticcheck
+    - tagalign
+    - tenv
+    - thelper
+    - tparallel
+    - typecheck
+    - unparam
+    - unused
+    - usestdlibvars
+    - wastedassign
+    - whitespace
+  disable-all: true
+issues:
+  max-issues-per-linter: 0
+  max-same-issues: 0
+run:
+  timeout: 5m
diff --git a/app.go b/app.go
index 4f1f31b..6e11f47 100644
--- a/app.go
+++ b/app.go
@@ -11,10 +11,7 @@ import (
 
 var (
 	ErrCommandNotSpecified = fmt.Errorf("command not specified")
-)
-
-var (
-	envarTransformRegexp = regexp.MustCompile(`[^a-zA-Z0-9_]+`)
+	envarTransformRegexp   = regexp.MustCompile(`[^a-zA-Z0-9_]+`)
 )
 
 type ApplicationValidator func(*Application) error
@@ -22,30 +19,24 @@ type ApplicationValidator func(*Application) error
 // An Application contains the definitions of flags, arguments and commands
 // for an application.
 type Application struct {
+	errorWriter   io.Writer
+	usageWriter   io.Writer
+	usageFuncs    template.FuncMap
+	VersionFlag   *FlagClause
+	HelpCommand   *CmdClause
+	HelpFlag      *FlagClause
+	terminate     func(status int)
+	validator     ApplicationValidator
+	usageTemplate string
+	version       string
+	author        string
+	Help          string
+	Name          string
 	cmdMixin
-	initialized bool
-
-	Name string
-	Help string
-
-	author         string
-	version        string
-	errorWriter    io.Writer // Destination for errors.
-	usageWriter    io.Writer // Destination for usage
-	usageTemplate  string
-	usageFuncs     template.FuncMap
-	validator      ApplicationValidator
-	terminate      func(status int) // See Terminate()
-	noInterspersed bool             // can flags be interspersed with args (or must they come first)
+	noInterspersed bool
 	defaultEnvars  bool
 	completion     bool
-
-	// Help flag. Exposed for user customisation.
-	HelpFlag *FlagClause
-	// Help command. Exposed for user customisation. May be nil.
-	HelpCommand *CmdClause
-	// Version flag. Exposed for user customisation. May be nil.
-	VersionFlag *FlagClause
+	initialized    bool
 }
 
 // New creates a new Kingpin application instance.
@@ -129,7 +120,7 @@ func (a *Application) Terminate(terminate func(int)) *Application {
 }
 
 // Writer specifies the writer to use for usage and errors. Defaults to os.Stderr.
-// DEPRECATED: See ErrorWriter and UsageWriter.
+// Deprecated: See ErrorWriter and UsageWriter.
 func (a *Application) Writer(w io.Writer) *Application {
 	a.errorWriter = w
 	a.usageWriter = w
@@ -189,9 +180,8 @@ func (a *Application) parseContext(ignoreDefault bool, args []string) (*ParseCon
 // This will populate all flag and argument values, call all callbacks, and so
 // on.
 func (a *Application) Parse(args []string) (command string, err error) {
-
 	context, parseErr := a.ParseContext(args)
-	selected := []string{}
+	var selected []string
 	var setValuesErr error
 
 	if context == nil {
@@ -239,8 +229,8 @@ func (a *Application) writeUsage(context *ParseContext, err error) {
 	if err != nil {
 		a.Errorf("%s", err)
 	}
-	if err := a.UsageForContext(context); err != nil {
-		panic(err)
+	if errUsage := a.UsageForContext(context); errUsage != nil {
+		panic(errUsage)
 	}
 	if err != nil {
 		a.terminate(1)
diff --git a/app_test.go b/app_test.go
index 27c95e5..3c519a4 100644
--- a/app_test.go
+++ b/app_test.go
@@ -2,14 +2,13 @@ package kingpin
 
 import (
 	"errors"
-	"io/ioutil"
-
-	"github.com/stretchr/testify/assert"
-
+	"io"
 	"sort"
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func newTestApp() *Application {
@@ -17,6 +16,7 @@ func newTestApp() *Application {
 }
 
 func TestCommander(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	ping := c.Command("ping", "Ping an IP address.")
 	pingTTL := ping.Flag("ttl", "TTL for ICMP packets").Short('t').Default("5s").Duration()
@@ -33,6 +33,7 @@ func TestCommander(t *testing.T) {
 }
 
 func TestRequiredFlags(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Flag("a", "a").String()
 	c.Flag("b", "b").Required().String()
@@ -44,6 +45,7 @@ func TestRequiredFlags(t *testing.T) {
 }
 
 func TestRepeatableFlags(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Flag("a", "a").String()
 	c.Flag("b", "b").Strings()
@@ -54,6 +56,7 @@ func TestRepeatableFlags(t *testing.T) {
 }
 
 func TestInvalidDefaultFlagValueErrors(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Flag("foo", "foo").Default("a").Int()
 	_, err := c.Parse([]string{})
@@ -61,6 +64,7 @@ func TestInvalidDefaultFlagValueErrors(t *testing.T) {
 }
 
 func TestInvalidDefaultArgValueErrors(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	cmd := c.Command("cmd", "cmd")
 	cmd.Arg("arg", "arg").Default("one").Int()
@@ -69,6 +73,7 @@ func TestInvalidDefaultArgValueErrors(t *testing.T) {
 }
 
 func TestArgsRequiredAfterNonRequiredErrors(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	cmd := c.Command("cmd", "")
 	cmd.Arg("a", "a").String()
@@ -78,7 +83,8 @@ func TestArgsRequiredAfterNonRequiredErrors(t *testing.T) {
 }
 
 func TestArgsMultipleRequiredThenNonRequired(t *testing.T) {
-	c := newTestApp().Writer(ioutil.Discard)
+	t.Parallel()
+	c := newTestApp().Writer(io.Discard)
 	cmd := c.Command("cmd", "")
 	cmd.Arg("a", "a").Required().String()
 	cmd.Arg("b", "b").Required().String()
@@ -91,6 +97,7 @@ func TestArgsMultipleRequiredThenNonRequired(t *testing.T) {
 }
 
 func TestDispatchCallbackIsCalled(t *testing.T) {
+	t.Parallel()
 	dispatched := false
 	c := newTestApp()
 	c.Command("cmd", "").Action(func(*ParseContext) error {
@@ -104,6 +111,7 @@ func TestDispatchCallbackIsCalled(t *testing.T) {
 }
 
 func TestTopLevelArgWorks(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	s := c.Arg("arg", "help").String()
 	_, err := c.Parse([]string{"foo"})
@@ -112,6 +120,7 @@ func TestTopLevelArgWorks(t *testing.T) {
 }
 
 func TestTopLevelArgCantBeUsedWithCommands(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Arg("arg", "help").String()
 	c.Command("cmd", "help")
@@ -120,6 +129,7 @@ func TestTopLevelArgCantBeUsedWithCommands(t *testing.T) {
 }
 
 func TestTooManyArgs(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	a.Arg("a", "").String()
 	_, err := a.Parse([]string{"a", "b"})
@@ -127,6 +137,7 @@ func TestTooManyArgs(t *testing.T) {
 }
 
 func TestTooManyArgsAfterCommand(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	a.Command("a", "")
 	assert.NoError(t, a.init())
@@ -135,6 +146,7 @@ func TestTooManyArgsAfterCommand(t *testing.T) {
 }
 
 func TestArgsLooksLikeFlagsWithConsumeRemainder(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	a.Arg("opts", "").Required().Strings()
 	_, err := a.Parse([]string{"hello", "-world"})
@@ -142,6 +154,7 @@ func TestArgsLooksLikeFlagsWithConsumeRemainder(t *testing.T) {
 }
 
 func TestCommandParseDoesNotResetFlagsToDefault(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	flag := app.Flag("flag", "").Default("default").String()
 	app.Command("cmd", "")
@@ -152,6 +165,7 @@ func TestCommandParseDoesNotResetFlagsToDefault(t *testing.T) {
 }
 
 func TestCommandParseDoesNotFailRequired(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	flag := app.Flag("flag", "").Required().String()
 	app.Command("cmd", "")
@@ -162,6 +176,7 @@ func TestCommandParseDoesNotFailRequired(t *testing.T) {
 }
 
 func TestSelectedCommand(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	c0 := app.Command("c0", "")
 	c0.Command("c1", "")
@@ -171,6 +186,7 @@ func TestSelectedCommand(t *testing.T) {
 }
 
 func TestSubCommandRequired(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	c0 := app.Command("c0", "")
 	c0.Command("c1", "")
@@ -179,6 +195,7 @@ func TestSubCommandRequired(t *testing.T) {
 }
 
 func TestInterspersedFalse(t *testing.T) {
+	t.Parallel()
 	app := newTestApp().Interspersed(false)
 	a1 := app.Arg("a1", "").String()
 	a2 := app.Arg("a2", "").String()
@@ -192,6 +209,7 @@ func TestInterspersedFalse(t *testing.T) {
 }
 
 func TestInterspersedTrue(t *testing.T) {
+	t.Parallel()
 	// test once with the default value and once with explicit true
 	for i := 0; i < 2; i++ {
 		app := newTestApp()
@@ -214,6 +232,7 @@ func TestInterspersedTrue(t *testing.T) {
 }
 
 func TestDefaultEnvars(t *testing.T) {
+	t.Parallel()
 	a := New("some-app", "").Terminate(nil).DefaultEnvars()
 	f0 := a.Flag("some-flag", "")
 	f0.Bool()
@@ -229,6 +248,7 @@ func TestDefaultEnvars(t *testing.T) {
 }
 
 func TestBashCompletionOptionsWithEmptyApp(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	context, err := a.ParseContext([]string{"--completion-bash"})
 	if err != nil {
@@ -239,6 +259,7 @@ func TestBashCompletionOptionsWithEmptyApp(t *testing.T) {
 }
 
 func TestBashCompletionOptions(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	a.Command("one", "")
 	a.Flag("flag-0", "").String()
@@ -411,10 +432,10 @@ func TestBashCompletionOptions(t *testing.T) {
 
 		assert.Equal(t, c.ExpectedOptions, args, "Expected != Actual: [%v] != [%v]. \nInput was: [%v]", c.ExpectedOptions, args, c.Args)
 	}
-
 }
 
 func TestCmdValidation(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	cmd := c.Command("cmd", "")
 
@@ -436,6 +457,7 @@ func TestCmdValidation(t *testing.T) {
 }
 
 func TestVersion(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Flag("config", "path to config file").Default("config.yaml").ExistingFile()
 	c.Version("1.0.0")
diff --git a/args.go b/args.go
index 54e4107..fc906b8 100644
--- a/args.go
+++ b/args.go
@@ -64,14 +64,14 @@ func (a *argGroup) init() error {
 }
 
 type ArgClause struct {
-	actionMixin
 	parserMixin
+	name        string
+	help        string
+	placeholder string
+	actionMixin
 	completionsMixin
 	envarMixin
-	name          string
-	help          string
 	defaultValues []string
-	placeholder   string
 	hidden        bool
 	required      bool
 }
@@ -129,7 +129,7 @@ func (a *ArgClause) Hidden() *ArgClause {
 }
 
 // PlaceHolder sets the place-holder string used for arg values in the help. The
-// default behaviour is to use the arg name between < > brackets.
+// default behavior is to use the arg name between < > brackets.
 func (a *ArgClause) PlaceHolder(value string) *ArgClause {
 	a.placeholder = value
 	return a
@@ -174,13 +174,13 @@ func (a *ArgClause) PreAction(action Action) *ArgClause {
 	return a
 }
 
-// HintAction registers a HintAction (function) for the arg to provide completions
+// HintAction registers a HintAction (function) for the arg to provide completions.
 func (a *ArgClause) HintAction(action HintAction) *ArgClause {
 	a.addHintAction(action)
 	return a
 }
 
-// HintOptions registers any number of options for the flag to provide completions
+// HintOptions registers any number of options for the flag to provide completions.
 func (a *ArgClause) HintOptions(options ...string) *ArgClause {
 	a.addHintAction(func() []string {
 		return options
diff --git a/args_test.go b/args_test.go
index 695b208..0207960 100644
--- a/args_test.go
+++ b/args_test.go
@@ -1,14 +1,14 @@
 package kingpin
 
 import (
-	"io/ioutil"
-	"os"
+	"io"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 )
 
 func TestArgRemainder(t *testing.T) {
+	t.Parallel()
 	app := New("test", "")
 	v := app.Arg("test", "").Strings()
 	args := []string{"hello", "world"}
@@ -18,6 +18,7 @@ func TestArgRemainder(t *testing.T) {
 }
 
 func TestArgRemainderErrorsWhenNotLast(t *testing.T) {
+	t.Parallel()
 	a := newArgGroup()
 	a.Arg("test", "").Strings()
 	a.Arg("test2", "").String()
@@ -25,9 +26,10 @@ func TestArgRemainderErrorsWhenNotLast(t *testing.T) {
 }
 
 func TestArgMultipleRequired(t *testing.T) {
+	t.Parallel()
 	terminated := false
 	app := New("test", "")
-	app.Version("0.0.0").Writer(ioutil.Discard)
+	app.Version("0.0.0").Writer(io.Discard)
 	app.Arg("a", "").Required().String()
 	app.Arg("b", "").Required().String()
 	app.Terminate(func(int) { terminated = true })
@@ -43,6 +45,7 @@ func TestArgMultipleRequired(t *testing.T) {
 }
 
 func TestInvalidArgsDefaultCanBeOverridden(t *testing.T) {
+	t.Parallel()
 	app := New("test", "")
 	app.Arg("a", "").Default("invalid").Bool()
 	_, err := app.Parse([]string{})
@@ -50,6 +53,7 @@ func TestInvalidArgsDefaultCanBeOverridden(t *testing.T) {
 }
 
 func TestArgMultipleValuesDefault(t *testing.T) {
+	t.Parallel()
 	app := New("test", "")
 	a := app.Arg("a", "").Default("default1", "default2").Strings()
 	_, err := app.Parse([]string{})
@@ -58,6 +62,7 @@ func TestArgMultipleValuesDefault(t *testing.T) {
 }
 
 func TestRequiredArgWithEnvarMissingErrors(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Arg("t", "").Envar("TEST_ARG_ENVAR").Required().Int()
 	_, err := app.Parse([]string{})
@@ -65,7 +70,7 @@ func TestRequiredArgWithEnvarMissingErrors(t *testing.T) {
 }
 
 func TestArgRequiredWithEnvar(t *testing.T) {
-	os.Setenv("TEST_ARG_ENVAR", "123")
+	t.Setenv("TEST_ARG_ENVAR", "123")
 	app := newTestApp()
 	flag := app.Arg("t", "").Envar("TEST_ARG_ENVAR").Required().Int()
 	_, err := app.Parse([]string{})
@@ -74,7 +79,7 @@ func TestArgRequiredWithEnvar(t *testing.T) {
 }
 
 func TestSubcommandArgRequiredWithEnvar(t *testing.T) {
-	os.Setenv("TEST_ARG_ENVAR", "123")
+	t.Setenv("TEST_ARG_ENVAR", "123")
 	app := newTestApp()
 	cmd := app.Command("command", "")
 	flag := cmd.Arg("t", "").Envar("TEST_ARG_ENVAR").Required().Int()
diff --git a/cmd.go b/cmd.go
index cd7e612..29adf85 100644
--- a/cmd.go
+++ b/cmd.go
@@ -124,7 +124,6 @@ func (c *cmdMixin) FlagCompletion(flagName string, flagValue string) (choices []
 	}
 	// No Flag directly matched.
 	return options, false, false
-
 }
 
 type cmdGroup struct {
@@ -166,16 +165,6 @@ func newCmdGroup(app *Application) *cmdGroup {
 	}
 }
 
-func (c *cmdGroup) flattenedCommands() (out []*CmdClause) {
-	for _, cmd := range c.commandOrder {
-		if len(cmd.commands) == 0 {
-			out = append(out, cmd)
-		}
-		out = append(out, cmd.flattenedCommands()...)
-	}
-	return
-}
-
 func (c *cmdGroup) addCommand(name, help string) *CmdClause {
 	cmd := newCommand(c.app, name, help)
 	c.commands[name] = cmd
@@ -222,16 +211,16 @@ type CmdClauseValidator func(*CmdClause) error
 // A CmdClause is a single top-level command. It encapsulates a set of flags
 // and either subcommands or positional arguments.
 type CmdClause struct {
+	app       *Application
+	validator CmdClauseValidator
+	name      string
+	help      string
+	helpLong  string
 	cmdMixin
-	app            *Application
-	name           string
 	aliases        []string
-	help           string
-	helpLong       string
+	completionAlts []string
 	isDefault      bool
-	validator      CmdClauseValidator
 	hidden         bool
-	completionAlts []string
 }
 
 func newCommand(app *Application, name, help string) *CmdClause {
diff --git a/cmd/genvalues/main.go b/cmd/genvalues/main.go
index a2c6fec..d7fb621 100644
--- a/cmd/genvalues/main.go
+++ b/cmd/genvalues/main.go
@@ -6,6 +6,9 @@ import (
 	"os/exec"
 	"strings"
 	"text/template"
+
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
 )
 
 const (
@@ -15,7 +18,7 @@ const (
 
 {{range .}}
 {{if not .NoValueParser}}
-// -- {{.Type}} Value
+// -- {{.Type}} Value.
 type {{.|ValueName}} struct { v *{{.Type}} }
 
 func new{{.|Name}}Value(p *{{.Type}}) *{{.|ValueName}} {
@@ -69,12 +72,12 @@ func (p *parserMixin) {{.|Plural}}Var(target *[]{{.Type}}) {
 
 type Value struct {
 	Name          string `json:"name"`
-	NoValueParser bool   `json:"no_value_parser"`
 	Type          string `json:"type"`
 	Parser        string `json:"parser"`
 	Format        string `json:"format"`
 	Plural        string `json:"plural"`
 	Help          string `json:"help"`
+	NoValueParser bool   `json:"no_value_parser"`
 }
 
 func fatalIfError(err error) {
@@ -92,11 +95,12 @@ func main() {
 	err = json.NewDecoder(r).Decode(&v)
 	fatalIfError(err)
 
+	c := cases.Title(language.English)
 	valueName := func(v *Value) string {
 		if v.Name != "" {
 			return v.Name
 		}
-		return strings.Title(v.Type)
+		return c.String(v.Type)
 	}
 
 	t, err := template.New("genvalues").Funcs(template.FuncMap{
diff --git a/cmd_test.go b/cmd_test.go
index 8f307a0..10e0942 100644
--- a/cmd_test.go
+++ b/cmd_test.go
@@ -3,10 +3,9 @@ package kingpin
 import (
 	"sort"
 	"strings"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
-
-	"testing"
 )
 
 func parseAndExecute(app *Application, context *ParseContext) (string, error) {
@@ -23,6 +22,7 @@ func parseAndExecute(app *Application, context *ParseContext) (string, error) {
 }
 
 func complete(t *testing.T, app *Application, args ...string) []string {
+	t.Helper()
 	context, err := app.ParseContext(args)
 	assert.NoError(t, err)
 	if err != nil {
@@ -36,6 +36,7 @@ func complete(t *testing.T, app *Application, args ...string) []string {
 }
 
 func TestNestedCommands(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	sub1 := app.Command("sub1", "")
 	sub1.Flag("sub1", "")
@@ -54,6 +55,7 @@ func TestNestedCommands(t *testing.T) {
 }
 
 func TestNestedCommandsWithArgs(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	cmd := app.Command("a", "").Command("b", "")
 	a := cmd.Arg("a", "").String()
@@ -68,6 +70,7 @@ func TestNestedCommandsWithArgs(t *testing.T) {
 }
 
 func TestNestedCommandsWithFlags(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	cmd := app.Command("a", "").Command("b", "")
 	a := cmd.Flag("aaa", "").Short('a').String()
@@ -84,6 +87,7 @@ func TestNestedCommandsWithFlags(t *testing.T) {
 }
 
 func TestNestedCommandWithMergedFlags(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	cmd0 := app.Command("a", "")
 	cmd0f0 := cmd0.Flag("aflag", "").Bool()
@@ -102,6 +106,7 @@ func TestNestedCommandWithMergedFlags(t *testing.T) {
 }
 
 func TestNestedCommandWithDuplicateFlagErrors(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	app.Flag("test", "").Bool()
 	app.Command("cmd0", "").Flag("test", "").Bool()
@@ -110,6 +115,7 @@ func TestNestedCommandWithDuplicateFlagErrors(t *testing.T) {
 }
 
 func TestNestedCommandWithArgAndMergedFlags(t *testing.T) {
+	t.Parallel()
 	app := New("app", "")
 	cmd0 := app.Command("a", "")
 	cmd0f0 := cmd0.Flag("aflag", "").Bool()
@@ -130,6 +136,7 @@ func TestNestedCommandWithArgAndMergedFlags(t *testing.T) {
 }
 
 func TestDefaultSubcommandEOL(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	c0 := app.Command("c0", "").Default()
 	c0.Command("c01", "").Default()
@@ -141,6 +148,7 @@ func TestDefaultSubcommandEOL(t *testing.T) {
 }
 
 func TestDefaultSubcommandWithArg(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	c0 := app.Command("c0", "").Default()
 	c01 := c0.Command("c01", "").Default()
@@ -155,6 +163,7 @@ func TestDefaultSubcommandWithArg(t *testing.T) {
 }
 
 func TestDefaultSubcommandWithFlags(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	c0 := app.Command("c0", "").Default()
 	_ = c0.Flag("f0", "").Int()
@@ -169,6 +178,7 @@ func TestDefaultSubcommandWithFlags(t *testing.T) {
 }
 
 func TestMultipleDefaultCommands(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Command("c0", "").Default()
 	app.Command("c1", "").Default()
@@ -177,6 +187,7 @@ func TestMultipleDefaultCommands(t *testing.T) {
 }
 
 func TestAliasedCommand(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Command("one", "").Alias("two")
 	selected, _ := app.Parse([]string{"one"})
@@ -188,6 +199,7 @@ func TestAliasedCommand(t *testing.T) {
 }
 
 func TestDuplicateAlias(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Command("one", "")
 	app.Command("two", "").Alias("one")
@@ -196,6 +208,7 @@ func TestDuplicateAlias(t *testing.T) {
 }
 
 func TestFlagCompletion(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Command("one", "")
 	two := app.Command("two", "")
@@ -204,12 +217,12 @@ func TestFlagCompletion(t *testing.T) {
 	two.Flag("flag-3", "")
 
 	cases := []struct {
-		target              cmdMixin
 		flagName            string
 		flagValue           string
+		target              cmdMixin
+		expectedFlags       []string
 		expectedFlagMatch   bool
 		expectedOptionMatch bool
-		expectedFlags       []string
 	}{
 		{
 			// Test top level flags
@@ -275,10 +288,10 @@ func TestFlagCompletion(t *testing.T) {
 		assert.Equal(t, c.expectedFlagMatch, flagMatch, "Test case %d: expectedFlagMatch != flagMatch", i+1)
 		assert.Equal(t, c.expectedOptionMatch, optionMatch, "Test case %d: expectedOptionMatch != optionMatch", i+1)
 	}
-
 }
 
 func TestCmdCompletion(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Command("one", "")
 	two := app.Command("two", "")
@@ -290,6 +303,7 @@ func TestCmdCompletion(t *testing.T) {
 }
 
 func TestHiddenCmdCompletion(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 
 	// top level visible & hidden cmds, with no sub-cmds
@@ -317,6 +331,7 @@ func TestHiddenCmdCompletion(t *testing.T) {
 }
 
 func TestDefaultCmdCompletion(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 
 	cmd1 := app.Command("cmd1", "")
@@ -375,6 +390,7 @@ func TestDefaultCmdCompletion(t *testing.T) {
 }
 
 func TestPartialCmdCompletion(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 
 	cmd1 := app.Command("cmd1", "")
@@ -388,7 +404,6 @@ func TestPartialCmdCompletion(t *testing.T) {
 	cmd4.Arg("cmd4-arg2", "").HintOptions("cmd4-arg2").String()
 	cmd4.Arg("cmd4-arg3", "").HintOptions("cmd4-arg3").String()
 
-
 	// partial matches
 	assert.Equal(t, []string{"cmd1-arg1-opt1", "cmd1-arg1-opt2", "cmd1-arg1-opt3"}, complete(t, app, "cmd1", "cmd1-arg1-opt"))
 	assert.Equal(t, []string{"cmd2-123456", "cmd2-123789", "cmd2-456789"}, complete(t, app, "cmd2", "cmd2-"))
diff --git a/completions.go b/completions.go
index 6e7b409..2221350 100644
--- a/completions.go
+++ b/completions.go
@@ -2,17 +2,19 @@ package kingpin
 
 // HintAction is a function type who is expected to return a slice of possible
 // command line arguments.
-type HintAction func() []string
-type completionsMixin struct {
-	hintActions        []HintAction
-	builtinHintActions []HintAction
-}
+type (
+	HintAction       func() []string
+	completionsMixin struct {
+		hintActions        []HintAction
+		builtinHintActions []HintAction
+	}
+)
 
 func (a *completionsMixin) addHintAction(action HintAction) {
 	a.hintActions = append(a.hintActions, action)
 }
 
-// Allow adding of HintActions which are added internally, ie, EnumVar
+// Allow adding of HintActions which are added internally, ie, EnumVar.
 func (a *completionsMixin) addHintActionBuiltin(action HintAction) {
 	a.builtinHintActions = append(a.builtinHintActions, action)
 }
diff --git a/completions_test.go b/completions_test.go
index 7da9c06..06eea77 100644
--- a/completions_test.go
+++ b/completions_test.go
@@ -7,6 +7,7 @@ import (
 )
 
 func TestResolveWithBuiltin(t *testing.T) {
+	t.Parallel()
 	a := completionsMixin{}
 
 	hintAction1 := func() []string {
@@ -23,6 +24,7 @@ func TestResolveWithBuiltin(t *testing.T) {
 }
 
 func TestResolveWithUser(t *testing.T) {
+	t.Parallel()
 	a := completionsMixin{}
 	hintAction1 := func() []string {
 		return []string{"opt1", "opt2"}
@@ -38,6 +40,7 @@ func TestResolveWithUser(t *testing.T) {
 }
 
 func TestResolveWithCombination(t *testing.T) {
+	t.Parallel()
 	a := completionsMixin{}
 	builtin := func() []string {
 		return []string{"opt1", "opt2"}
@@ -55,6 +58,7 @@ func TestResolveWithCombination(t *testing.T) {
 }
 
 func TestAddHintAction(t *testing.T) {
+	t.Parallel()
 	a := completionsMixin{}
 	hintFunc := func() []string {
 		return []string{"opt1", "opt2"}
@@ -66,6 +70,7 @@ func TestAddHintAction(t *testing.T) {
 }
 
 func TestAddHintActionBuiltin(t *testing.T) {
+	t.Parallel()
 	a := completionsMixin{}
 	hintFunc := func() []string {
 		return []string{"opt1", "opt2"}
diff --git a/doc.go b/doc.go
index 8a72729..a8ca25d 100644
--- a/doc.go
+++ b/doc.go
@@ -1,68 +1,68 @@
 // Package kingpin provides command line interfaces like this:
 //
-//     $ chat
-//     usage: chat [<flags>] <command> [<flags>] [<args> ...]
+//	$ chat
+//	usage: chat [<flags>] <command> [<flags>] [<args> ...]
 //
-//     Flags:
-//       --debug              enable debug mode
-//       --help               Show help.
-//       --server=127.0.0.1   server address
+//	Flags:
+//	  --debug              enable debug mode
+//	  --help               Show help.
+//	  --server=127.0.0.1   server address
 //
-//     Commands:
-//       help <command>
-//         Show help for a command.
+//	Commands:
+//	  help <command>
+//	    Show help for a command.
 //
-//       post [<flags>] <channel>
-//         Post a message to a channel.
+//	  post [<flags>] <channel>
+//	    Post a message to a channel.
 //
-//       register <nick> <name>
-//         Register a new user.
+//	  register <nick> <name>
+//	    Register a new user.
 //
-//     $ chat help post
-//     usage: chat [<flags>] post [<flags>] <channel> [<text>]
+//	$ chat help post
+//	usage: chat [<flags>] post [<flags>] <channel> [<text>]
 //
-//     Post a message to a channel.
+//	Post a message to a channel.
 //
-//     Flags:
-//       --image=IMAGE   image to post
+//	Flags:
+//	  --image=IMAGE   image to post
 //
-//     Args:
-//       <channel>   channel to post to
-//       [<text>]    text to post
-//     $ chat post --image=~/Downloads/owls.jpg pics
+//	Args:
+//	  <channel>   channel to post to
+//	  [<text>]    text to post
+//	$ chat post --image=~/Downloads/owls.jpg pics
 //
 // From code like this:
 //
-//     package main
-//
-//     import "github.com/alecthomas/kingpin/v2"
-//
-//     var (
-//       debug    = kingpin.Flag("debug", "enable debug mode").Default("false").Bool()
-//       serverIP = kingpin.Flag("server", "server address").Default("127.0.0.1").IP()
-//
-//       register     = kingpin.Command("register", "Register a new user.")
-//       registerNick = register.Arg("nick", "nickname for user").Required().String()
-//       registerName = register.Arg("name", "name of user").Required().String()
-//
-//       post        = kingpin.Command("post", "Post a message to a channel.")
-//       postImage   = post.Flag("image", "image to post").ExistingFile()
-//       postChannel = post.Arg("channel", "channel to post to").Required().String()
-//       postText    = post.Arg("text", "text to post").String()
-//     )
-//
-//     func main() {
-//       switch kingpin.Parse() {
-//       // Register user
-//       case "register":
-//         println(*registerNick)
-//
-//       // Post message
-//       case "post":
-//         if *postImage != nil {
-//         }
-//         if *postText != "" {
-//         }
-//       }
-//     }
+//	package main
+//
+//	import "github.com/alecthomas/kingpin/v2"
+//
+//	var (
+//	  debug    = kingpin.Flag("debug", "enable debug mode").Default("false").Bool()
+//	  serverIP = kingpin.Flag("server", "server address").Default("127.0.0.1").IP()
+//
+//	  register     = kingpin.Command("register", "Register a new user.")
+//	  registerNick = register.Arg("nick", "nickname for user").Required().String()
+//	  registerName = register.Arg("name", "name of user").Required().String()
+//
+//	  post        = kingpin.Command("post", "Post a message to a channel.")
+//	  postImage   = post.Flag("image", "image to post").ExistingFile()
+//	  postChannel = post.Arg("channel", "channel to post to").Required().String()
+//	  postText    = post.Arg("text", "text to post").String()
+//	)
+//
+//	func main() {
+//	  switch kingpin.Parse() {
+//	  // Register user
+//	  case "register":
+//	    println(*registerNick)
+//
+//	  // Post message
+//	  case "post":
+//	    if *postImage != nil {
+//	    }
+//	    if *postText != "" {
+//	    }
+//	  }
+//	}
 package kingpin
diff --git a/flags.go b/flags.go
index 2b2938b..ecb0621 100644
--- a/flags.go
+++ b/flags.go
@@ -82,7 +82,7 @@ loop:
 
 		case TokenLong, TokenShort:
 			flagToken := token
-			defaultValue := ""
+			var defaultValue string
 			var flag *FlagClause
 			var ok bool
 			invert := false
@@ -144,17 +144,17 @@ loop:
 
 // FlagClause is a fluid interface used to build flags.
 type FlagClause struct {
+	setByUser *bool
 	parserMixin
+	name        string
+	help        string
+	placeholder string
 	actionMixin
 	completionsMixin
 	envarMixin
-	name          string
-	shorthand     rune
-	help          string
 	defaultValues []string
-	placeholder   string
+	shorthand     rune
 	hidden        bool
-	setByUser     *bool
 }
 
 func newFlag(name, help string) *FlagClause {
@@ -227,13 +227,13 @@ func (f *FlagClause) PreAction(action Action) *FlagClause {
 	return f
 }
 
-// HintAction registers a HintAction (function) for the flag to provide completions
+// HintAction registers a HintAction (function) for the flag to provide completions.
 func (a *FlagClause) HintAction(action HintAction) *FlagClause {
 	a.addHintAction(action)
 	return a
 }
 
-// HintOptions registers any number of options for the flag to provide completions
+// HintOptions registers any number of options for the flag to provide completions.
 func (a *FlagClause) HintOptions(options ...string) *FlagClause {
 	a.addHintAction(func() []string {
 		return options
@@ -255,7 +255,7 @@ func (a *FlagClause) Enum(options ...string) (target *string) {
 	return a.parserMixin.Enum(options...)
 }
 
-// IsSetByUser let to know if the flag was set by the user
+// IsSetByUser let to know if the flag was set by the user.
 func (f *FlagClause) IsSetByUser(setByUser *bool) *FlagClause {
 	if setByUser != nil {
 		*setByUser = false
@@ -270,7 +270,7 @@ func (f *FlagClause) Default(values ...string) *FlagClause {
 	return f
 }
 
-// DEPRECATED: Use Envar(name) instead.
+// Deprecated: Use Envar(name) instead.
 func (f *FlagClause) OverrideDefaultFromEnvar(envar string) *FlagClause {
 	return f.Envar(envar)
 }
@@ -293,7 +293,7 @@ func (f *FlagClause) NoEnvar() *FlagClause {
 }
 
 // PlaceHolder sets the place-holder string used for flag values in the help. The
-// default behaviour is to use the value provided by Default() if provided,
+// default behavior is to use the value provided by Default() if provided,
 // then fall back on the capitalized flag name.
 func (f *FlagClause) PlaceHolder(placeholder string) *FlagClause {
 	f.placeholder = placeholder
diff --git a/flags_test.go b/flags_test.go
index 1d28e14..f08b3bf 100644
--- a/flags_test.go
+++ b/flags_test.go
@@ -1,15 +1,14 @@
 package kingpin
 
 import (
-	"io/ioutil"
-	"os"
+	"io"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
-
-	"testing"
 )
 
 func TestBool(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	b := app.Flag("b", "").Bool()
 	_, err := app.Parse([]string{"--b"})
@@ -18,6 +17,7 @@ func TestBool(t *testing.T) {
 }
 
 func TestNoBool(t *testing.T) {
+	t.Parallel()
 	fg := newFlagGroup()
 	f := fg.Flag("b", "").Default("true")
 	b := f.Bool()
@@ -29,6 +29,7 @@ func TestNoBool(t *testing.T) {
 }
 
 func TestNegateNonBool(t *testing.T) {
+	t.Parallel()
 	fg := newFlagGroup()
 	f := fg.Flag("b", "")
 	f.Int()
@@ -39,6 +40,7 @@ func TestNegateNonBool(t *testing.T) {
 }
 
 func TestNegativePrefixLongFlag(t *testing.T) {
+	t.Parallel()
 	fg := newFlagGroup()
 	f := fg.Flag("no-comment", "")
 	b := f.Bool()
@@ -50,6 +52,7 @@ func TestNegativePrefixLongFlag(t *testing.T) {
 }
 
 func TestInvalidFlagDefaultCanBeOverridden(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Flag("a", "").Default("invalid").Bool()
 	_, err := app.Parse([]string{})
@@ -57,8 +60,9 @@ func TestInvalidFlagDefaultCanBeOverridden(t *testing.T) {
 }
 
 func TestRequiredFlag(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
-	app.Version("0.0.0").Writer(ioutil.Discard)
+	app.Version("0.0.0").Writer(io.Discard)
 	exits := 0
 	app.Terminate(func(int) { exits++ })
 	app.Flag("a", "").Required().Bool()
@@ -71,6 +75,7 @@ func TestRequiredFlag(t *testing.T) {
 }
 
 func TestShortFlag(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	f := app.Flag("long", "").Short('s').Bool()
 	_, err := app.Parse([]string{"-s"})
@@ -79,6 +84,7 @@ func TestShortFlag(t *testing.T) {
 }
 
 func TestUnicodeShortFlag(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	f := app.Flag("aaa", "").Short('ä').Bool()
 	_, err := app.Parse([]string{"-ä"})
@@ -87,6 +93,7 @@ func TestUnicodeShortFlag(t *testing.T) {
 }
 
 func TestCombinedShortFlags(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("short0", "").Short('0').Bool()
 	b := app.Flag("short1", "").Short('1').Bool()
@@ -99,6 +106,7 @@ func TestCombinedShortFlags(t *testing.T) {
 }
 
 func TestCombinedUnicodeShortFlags(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("short0", "").Short('0').Bool()
 	b := app.Flag("short1", "").Short('1').Bool()
@@ -113,6 +121,7 @@ func TestCombinedUnicodeShortFlags(t *testing.T) {
 }
 
 func TestCombinedShortFlagArg(t *testing.T) {
+	t.Parallel()
 	a := newTestApp()
 	n := a.Flag("short", "").Short('s').Int()
 	_, err := a.Parse([]string{"-s10"})
@@ -121,6 +130,7 @@ func TestCombinedShortFlagArg(t *testing.T) {
 }
 
 func TestCombinedUnicodeShortFlagArg(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("short", "").Short('ä').Int()
 	_, err := app.Parse([]string{"-ä10"})
@@ -129,6 +139,7 @@ func TestCombinedUnicodeShortFlagArg(t *testing.T) {
 }
 
 func TestCombinedUnicodeShortFlagUnicodeArg(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("short", "").Short('ä').String()
 	_, err := app.Parse([]string{"-äöö"})
@@ -137,11 +148,13 @@ func TestCombinedUnicodeShortFlagUnicodeArg(t *testing.T) {
 }
 
 func TestEmptyShortFlagIsAnError(t *testing.T) {
+	t.Parallel()
 	_, err := newTestApp().Parse([]string{"-"})
 	assert.Error(t, err)
 }
 
 func TestRequiredWithEnvarMissingErrors(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Flag("t", "").Envar("TEST_ENVAR").Required().Int()
 	_, err := app.Parse([]string{})
@@ -149,7 +162,7 @@ func TestRequiredWithEnvarMissingErrors(t *testing.T) {
 }
 
 func TestRequiredWithEnvar(t *testing.T) {
-	os.Setenv("TEST_ENVAR", "123")
+	t.Setenv("TEST_ENVAR", "123")
 	app := newTestApp()
 	flag := app.Flag("t", "").Envar("TEST_ENVAR").Required().Int()
 	_, err := app.Parse([]string{})
@@ -158,7 +171,7 @@ func TestRequiredWithEnvar(t *testing.T) {
 }
 
 func TestSubcommandFlagRequiredWithEnvar(t *testing.T) {
-	os.Setenv("TEST_ENVAR", "123")
+	t.Setenv("TEST_ENVAR", "123")
 	app := newTestApp()
 	cmd := app.Command("command", "")
 	flag := cmd.Flag("t", "").Envar("TEST_ENVAR").Required().Int()
@@ -168,6 +181,7 @@ func TestSubcommandFlagRequiredWithEnvar(t *testing.T) {
 }
 
 func TestRegexp(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	flag := app.Flag("reg", "").Regexp()
 	_, err := app.Parse([]string{"--reg", "^abc$"})
@@ -179,6 +193,7 @@ func TestRegexp(t *testing.T) {
 }
 
 func TestDuplicateShortFlag(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Flag("a", "").Short('a').String()
 	app.Flag("b", "").Short('a').String()
@@ -187,6 +202,7 @@ func TestDuplicateShortFlag(t *testing.T) {
 }
 
 func TestDuplicateLongFlag(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Flag("a", "").String()
 	app.Flag("a", "").String()
@@ -195,6 +211,7 @@ func TestDuplicateLongFlag(t *testing.T) {
 }
 
 func TestGetFlagAndOverrideDefault(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("a", "").Default("default").String()
 	_, err := app.Parse([]string{})
@@ -207,7 +224,7 @@ func TestGetFlagAndOverrideDefault(t *testing.T) {
 }
 
 func TestEnvarOverrideDefault(t *testing.T) {
-	os.Setenv("TEST_ENVAR", "123")
+	t.Setenv("TEST_ENVAR", "123")
 	app := newTestApp()
 	flag := app.Flag("t", "").Default("default").Envar("TEST_ENVAR").String()
 	_, err := app.Parse([]string{})
@@ -216,6 +233,7 @@ func TestEnvarOverrideDefault(t *testing.T) {
 }
 
 func TestFlagMultipleValuesDefault(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	a := app.Flag("a", "").Default("default1", "default2").Strings()
 	_, err := app.Parse([]string{})
@@ -224,6 +242,7 @@ func TestFlagMultipleValuesDefault(t *testing.T) {
 }
 
 func TestFlagMultipleValuesDefaultNonRepeatable(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	c.Flag("foo", "foo").Default("a", "b").String()
 	_, err := c.Parse([]string{})
@@ -233,7 +252,7 @@ func TestFlagMultipleValuesDefaultNonRepeatable(t *testing.T) {
 func TestFlagMultipleValuesDefaultEnvarUnix(t *testing.T) {
 	app := newTestApp()
 	a := app.Flag("a", "").Envar("TEST_MULTIPLE_VALUES").Strings()
-	os.Setenv("TEST_MULTIPLE_VALUES", "123\n456\n")
+	t.Setenv("TEST_MULTIPLE_VALUES", "123\n456\n")
 	_, err := app.Parse([]string{})
 	assert.NoError(t, err)
 	assert.Equal(t, []string{"123", "456"}, *a)
@@ -242,7 +261,7 @@ func TestFlagMultipleValuesDefaultEnvarUnix(t *testing.T) {
 func TestFlagMultipleValuesDefaultEnvarWindows(t *testing.T) {
 	app := newTestApp()
 	a := app.Flag("a", "").Envar("TEST_MULTIPLE_VALUES").Strings()
-	os.Setenv("TEST_MULTIPLE_VALUES", "123\r\n456\r\n")
+	t.Setenv("TEST_MULTIPLE_VALUES", "123\r\n456\r\n")
 	_, err := app.Parse([]string{})
 	assert.NoError(t, err)
 	assert.Equal(t, []string{"123", "456"}, *a)
@@ -251,13 +270,14 @@ func TestFlagMultipleValuesDefaultEnvarWindows(t *testing.T) {
 func TestFlagMultipleValuesDefaultEnvarNonRepeatable(t *testing.T) {
 	c := newTestApp()
 	a := c.Flag("foo", "foo").Envar("TEST_MULTIPLE_VALUES_NON_REPEATABLE").String()
-	os.Setenv("TEST_MULTIPLE_VALUES_NON_REPEATABLE", "123\n456")
+	t.Setenv("TEST_MULTIPLE_VALUES_NON_REPEATABLE", "123\n456")
 	_, err := c.Parse([]string{})
 	assert.NoError(t, err)
 	assert.Equal(t, "123\n456", *a)
 }
 
 func TestFlagHintAction(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 
 	action := func() []string {
@@ -270,6 +290,7 @@ func TestFlagHintAction(t *testing.T) {
 }
 
 func TestFlagHintOptions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 
 	a := c.Flag("foo", "foo").HintOptions("opt1", "opt2")
@@ -278,6 +299,7 @@ func TestFlagHintOptions(t *testing.T) {
 }
 
 func TestFlagEnumVar(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	var bar string
 
@@ -294,13 +316,16 @@ func TestFlagEnumVar(t *testing.T) {
 }
 
 func TestMultiHintOptions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 
 	a := c.Flag("foo", "foo").HintOptions("opt1").HintOptions("opt2")
 	args := a.resolveCompletions()
 	assert.Equal(t, []string{"opt1", "opt2"}, args)
 }
+
 func TestMultiHintActions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 
 	a := c.Flag("foo", "foo").
@@ -315,6 +340,7 @@ func TestMultiHintActions(t *testing.T) {
 }
 
 func TestCombinationHintActionsOptions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 
 	a := c.Flag("foo", "foo").HintAction(func() []string {
@@ -325,6 +351,7 @@ func TestCombinationHintActionsOptions(t *testing.T) {
 }
 
 func TestCombinationEnumActions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	var foo string
 
@@ -349,6 +376,7 @@ func TestCombinationEnumActions(t *testing.T) {
 }
 
 func TestCombinationEnumOptions(t *testing.T) {
+	t.Parallel()
 	c := newTestApp()
 	var foo string
 
@@ -364,10 +392,10 @@ func TestCombinationEnumOptions(t *testing.T) {
 
 	args = b.resolveCompletions()
 	assert.Equal(t, []string{"opt5", "opt6"}, args)
-
 }
 
 func TestIsSetByUser(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	var isSet bool
 	b := app.Flag("b", "").IsSetByUser(&isSet).Bool()
diff --git a/go.mod b/go.mod
index bef9c21..fb79e98 100644
--- a/go.mod
+++ b/go.mod
@@ -6,6 +6,7 @@ require (
 	github.com/alecthomas/units v0.0.0-20240626203959-61d1e3462e30
 	github.com/stretchr/testify v1.9.0
 	github.com/xhit/go-str2duration/v2 v2.1.0
+	golang.org/x/text v0.16.0
 )
 
 require (
diff --git a/go.sum b/go.sum
index d8e9ead..1d8428e 100644
--- a/go.sum
+++ b/go.sum
@@ -3,6 +3,7 @@ github.com/alecthomas/units v0.0.0-20240626203959-61d1e3462e30/go.mod h1:fvzegU4
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -16,6 +17,66 @@ github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsT
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 github.com/xhit/go-str2duration/v2 v2.1.0 h1:lxklc02Drh6ynqX+DdPyp5pCKLUQpRT8bp8Ydu2Bstc=
 github.com/xhit/go-str2duration/v2 v2.1.0/go.mod h1:ohY8p+0f07DiV6Em5LKB0s2YpLtXVyJfNt1+BlmyAsU=
+github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
+golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
+golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
+golang.org/x/crypto v0.23.0/go.mod h1:CKFgDieR+mRhux2Lsu27y0fO304Db0wZe70UKqHu0v8=
+golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
+golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/mod v0.15.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/mod v0.17.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
+golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
+golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
+golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
+golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
+golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
+golang.org/x/net v0.25.0/go.mod h1:JkAGAh7GEvH74S6FOH42FLoXpXbE/aqXSrIQjXgsiwM=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
+golang.org/x/sync v0.6.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/telemetry v0.0.0-20240228155512-f48c80bd79b2/go.mod h1:TeRTkGYfJXctD9OcfyVLyj2J3IxLnKwHJR8f4D8a3YE=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
+golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
+golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
+golang.org/x/term v0.12.0/go.mod h1:owVbMEjm3cBLCHdkQu9b1opXd4ETQWc3BhuQGKgXgvU=
+golang.org/x/term v0.17.0/go.mod h1:lLRBjIVuehSbZlaOtGMbcMncT+aqLLLmKrsjNrUguwk=
+golang.org/x/term v0.20.0/go.mod h1:8UkIAJTvZgivsXaD6/pH6U9ecQzZ45awqEOzuCvwpFY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
+golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
+golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
+golang.org/x/text v0.13.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
+golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
+golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=
+golang.org/x/text v0.16.0/go.mod h1:GhwF1Be+LQoKShO3cGOHzqOgRrGaYc9AvblQOmPVHnI=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
+golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
+golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
+golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/guesswidth_unix.go b/guesswidth_unix.go
index ad8163f..3429240 100644
--- a/guesswidth_unix.go
+++ b/guesswidth_unix.go
@@ -1,3 +1,4 @@
+//go:build (!appengine && linux) || freebsd || darwin || dragonfly || netbsd || openbsd
 // +build !appengine,linux freebsd darwin dragonfly netbsd openbsd
 
 package kingpin
diff --git a/model.go b/model.go
index 382616c..d3659d8 100644
--- a/model.go
+++ b/model.go
@@ -8,16 +8,14 @@ import (
 
 // Data model for Kingpin command-line structure.
 
-var (
-	ignoreInCount = map[string]bool{
-		"help":                   true,
-		"help-long":              true,
-		"help-man":               true,
-		"completion-bash":        true,
-		"completion-script-bash": true,
-		"completion-script-zsh":  true,
-	}
-)
+var ignoreInCount = map[string]bool{
+	"help":                   true,
+	"help-long":              true,
+	"help-man":               true,
+	"completion-bash":        true,
+	"completion-script-bash": true,
+	"completion-script-zsh":  true,
+}
 
 type FlagGroupModel struct {
 	Flags []*FlagModel
@@ -28,7 +26,6 @@ func (f *FlagGroupModel) FlagSummary() string {
 	count := 0
 
 	for _, flag := range f.Flags {
-
 		if !ignoreInCount[flag.Name] {
 			count++
 		}
@@ -48,15 +45,15 @@ func (f *FlagGroupModel) FlagSummary() string {
 }
 
 type FlagModel struct {
+	Value       Value
 	Name        string
 	Help        string
-	Short       rune
-	Default     []string
 	Envar       string
 	PlaceHolder string
+	Default     []string
+	Short       rune
 	Required    bool
 	Hidden      bool
-	Value       Value
 }
 
 func (f *FlagModel) String() string {
@@ -129,14 +126,14 @@ func (a *ArgModel) HelpWithEnvar() string {
 }
 
 type ArgModel struct {
+	Value       Value
 	Name        string
 	Help        string
-	Default     []string
 	Envar       string
 	PlaceHolder string
+	Default     []string
 	Required    bool
 	Hidden      bool
-	Value       Value
 }
 
 func (a *ArgModel) String() string {
@@ -162,17 +159,17 @@ func (c *CmdGroupModel) FlattenedCommands() (out []*CmdModel) {
 }
 
 type CmdModel struct {
+	*FlagGroupModel
+	*ArgGroupModel
+	*CmdGroupModel
 	Name        string
-	Aliases     []string
 	Help        string
 	HelpLong    string
 	FullCommand string
+	Aliases     []string
 	Depth       int
 	Hidden      bool
 	Default     bool
-	*FlagGroupModel
-	*ArgGroupModel
-	*CmdGroupModel
 }
 
 func (c *CmdModel) String() string {
@@ -180,13 +177,13 @@ func (c *CmdModel) String() string {
 }
 
 type ApplicationModel struct {
+	*ArgGroupModel
+	*CmdGroupModel
+	*FlagGroupModel
 	Name    string
 	Help    string
 	Version string
 	Author  string
-	*ArgGroupModel
-	*CmdGroupModel
-	*FlagGroupModel
 }
 
 func (a *Application) Model() *ApplicationModel {
diff --git a/parser.go b/parser.go
index 5f28c78..6ccce94 100644
--- a/parser.go
+++ b/parser.go
@@ -35,14 +35,12 @@ func (t TokenType) String() string {
 	return "?"
 }
 
-var (
-	TokenEOLMarker = Token{-1, TokenEOL, ""}
-)
+var TokenEOLMarker = Token{Value: "", Index: -1, Type: TokenEOL}
 
 type Token struct {
+	Value string
 	Index int
 	Type  TokenType
-	Value string
 }
 
 func (t *Token) Equal(o *Token) bool {
@@ -88,17 +86,16 @@ type ParseElement struct {
 // any).
 type ParseContext struct {
 	SelectedCommand *CmdClause
-	ignoreDefault   bool
-	argsOnly        bool
+	flags           *flagGroup
+	arguments       *argGroup
 	peek            []*Token
-	argi            int // Index of current command-line arg we're processing.
 	args            []string
 	rawArgs         []string
-	flags           *flagGroup
-	arguments       *argGroup
-	argumenti       int // Cursor into arguments
-	// Flags, arguments and commands encountered and collected during parse.
-	Elements []*ParseElement
+	Elements        []*ParseElement
+	argi            int
+	argumenti       int
+	ignoreDefault   bool
+	argsOnly        bool
 }
 
 func (p *ParseContext) nextArg() *ArgClause {
@@ -174,7 +171,7 @@ func (p *ParseContext) Next() *Token {
 	p.next()
 
 	if p.argsOnly {
-		return &Token{p.argi, TokenArg, arg}
+		return &Token{Index: p.argi, Type: TokenArg, Value: arg}
 	}
 
 	if arg == "--" {
@@ -183,9 +180,9 @@ func (p *ParseContext) Next() *Token {
 
 	if strings.HasPrefix(arg, "--") {
 		parts := strings.SplitN(arg[2:], "=", 2)
-		token := &Token{p.argi, TokenLong, parts[0]}
+		token := &Token{Index: p.argi, Type: TokenLong, Value: parts[0]}
 		if len(parts) == 2 {
-			p.Push(&Token{p.argi, TokenArg, parts[1]})
+			p.Push(&Token{Index: p.argi, Type: TokenArg, Value: parts[1]})
 		}
 		return token
 	}
@@ -203,9 +200,9 @@ func (p *ParseContext) Next() *Token {
 			// Bool short flag.
 		} else {
 			// Short flag with combined argument: -fARG
-			token := &Token{p.argi, TokenShort, short}
+			token := &Token{Index: p.argi, Type: TokenShort, Value: short}
 			if len(arg) > size+1 {
-				p.Push(&Token{p.argi, TokenArg, arg[size+1:]})
+				p.Push(&Token{Index: p.argi, Type: TokenArg, Value: arg[size+1:]})
 			}
 			return token
 		}
@@ -213,11 +210,11 @@ func (p *ParseContext) Next() *Token {
 		if len(arg) > size+1 {
 			p.args = append([]string{"-" + arg[size+1:]}, p.args...)
 		}
-		return &Token{p.argi, TokenShort, short}
+		return &Token{Index: p.argi, Type: TokenShort, Value: short}
 	} else if EnableFileExpansion && strings.HasPrefix(arg, "@") {
 		expanded, err := ExpandArgsFromFile(arg[1:])
 		if err != nil {
-			return &Token{p.argi, TokenError, err.Error()}
+			return &Token{Index: p.argi, Type: TokenError, Value: err.Error()}
 		}
 		if len(p.args) == 0 {
 			p.args = expanded
@@ -227,7 +224,7 @@ func (p *ParseContext) Next() *Token {
 		return p.Next()
 	}
 
-	return &Token{p.argi, TokenArg, arg}
+	return &Token{Index: p.argi, Type: TokenArg, Value: arg}
 }
 
 func (p *ParseContext) Peek() *Token {
@@ -321,7 +318,8 @@ loop:
 			}
 
 		case TokenArg:
-			if cmds.have() {
+			switch {
+			case cmds.have():
 				selectedDefault := false
 				cmd, ok := cmds.commands[token.String()]
 				if !ok {
@@ -344,7 +342,7 @@ loop:
 				if !selectedDefault {
 					context.Next()
 				}
-			} else if context.arguments.have() {
+			case context.arguments.have():
 				if app.noInterspersed {
 					// no more flags
 					context.argsOnly = true
@@ -355,7 +353,7 @@ loop:
 				}
 				context.matchedArg(arg, token.String())
 				context.Next()
-			} else {
+			default:
 				break loop
 			}
 
diff --git a/parser_test.go b/parser_test.go
index 43dfde9..c72cc2c 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -1,7 +1,6 @@
 package kingpin
 
 import (
-	"io/ioutil"
 	"os"
 	"testing"
 
@@ -9,7 +8,8 @@ import (
 )
 
 func TestParserExpandFromFile(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	assert.NoError(t, err)
 	defer os.Remove(f.Name())
 	f.WriteString("hello\nworld\n")
@@ -26,7 +26,8 @@ func TestParserExpandFromFile(t *testing.T) {
 }
 
 func TestParserExpandFromFileLeadingArg(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	assert.NoError(t, err)
 	defer os.Remove(f.Name())
 	f.WriteString("hello\nworld\n")
@@ -45,7 +46,8 @@ func TestParserExpandFromFileLeadingArg(t *testing.T) {
 }
 
 func TestParserExpandFromFileTrailingArg(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	assert.NoError(t, err)
 	defer os.Remove(f.Name())
 	f.WriteString("hello\nworld\n")
@@ -64,7 +66,8 @@ func TestParserExpandFromFileTrailingArg(t *testing.T) {
 }
 
 func TestParserExpandFromFileMultipleSurroundingArgs(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	assert.NoError(t, err)
 	defer os.Remove(f.Name())
 	f.WriteString("hello\nworld\n")
@@ -85,7 +88,8 @@ func TestParserExpandFromFileMultipleSurroundingArgs(t *testing.T) {
 }
 
 func TestParserExpandFromFileMultipleFlags(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	assert.NoError(t, err)
 	defer os.Remove(f.Name())
 	f.WriteString("--flag1=f1\n--flag2=f2\n")
@@ -106,6 +110,7 @@ func TestParserExpandFromFileMultipleFlags(t *testing.T) {
 }
 
 func TestParseContextPush(t *testing.T) {
+	t.Parallel()
 	app := New("test", "")
 	app.Command("foo", "").Command("bar", "")
 	c := tokenize([]string{"foo", "bar"}, false)
diff --git a/parsers.go b/parsers.go
index 5a06882..02add63 100644
--- a/parsers.go
+++ b/parsers.go
@@ -40,7 +40,7 @@ func (p *parserMixin) Duration() (target *time.Duration) {
 	return
 }
 
-// Bytes parses numeric byte units. eg. 1.5KB
+// Bytes parses numeric byte units. eg. 1.5KB.
 func (p *parserMixin) Bytes() (target *units.Base2Bytes) {
 	target = new(units.Base2Bytes)
 	p.BytesVar(target)
@@ -128,7 +128,7 @@ func (p *parserMixin) DurationVar(target *time.Duration) {
 	p.SetValue(newDurationValue(target))
 }
 
-// BytesVar parses numeric byte units. eg. 1.5KB
+// BytesVar parses numeric byte units. eg. 1.5KB.
 func (p *parserMixin) BytesVar(target *units.Base2Bytes) {
 	p.SetValue(newBytesValue(target))
 }
@@ -158,7 +158,7 @@ func (p *parserMixin) FileVar(target **os.File) {
 	p.SetValue(newFileValue(target, os.O_RDONLY, 0))
 }
 
-// OpenFileVar calls os.OpenFile(flag, perm)
+// OpenFileVar calls os.OpenFile(flag, perm).
 func (p *parserMixin) OpenFileVar(target **os.File, flag int, perm os.FileMode) {
 	p.SetValue(newFileValue(target, flag, perm))
 }
diff --git a/parsers_test.go b/parsers_test.go
index 81708c7..fe60e26 100644
--- a/parsers_test.go
+++ b/parsers_test.go
@@ -1,17 +1,16 @@
 package kingpin
 
 import (
-	"io/ioutil"
 	"net"
 	"net/url"
 	"os"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
-
-	"testing"
 )
 
 func TestParseStrings(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.Strings()
 	p.value.Set("a")
@@ -20,6 +19,7 @@ func TestParseStrings(t *testing.T) {
 }
 
 func TestStringsStringer(t *testing.T) {
+	t.Parallel()
 	target := []string{}
 	v := newAccumulator(&target, func(v interface{}) Value { return newStringValue(v.(*string)) })
 	v.Set("hello")
@@ -28,6 +28,7 @@ func TestStringsStringer(t *testing.T) {
 }
 
 func TestParseStringMap(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.StringMap()
 	p.value.Set("a:b")
@@ -36,6 +37,7 @@ func TestParseStringMap(t *testing.T) {
 }
 
 func TestParseIP(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.IP()
 	p.value.Set("10.1.1.2")
@@ -44,6 +46,7 @@ func TestParseIP(t *testing.T) {
 }
 
 func TestParseURL(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.URL()
 	p.value.Set("http://w3.org")
@@ -53,7 +56,8 @@ func TestParseURL(t *testing.T) {
 }
 
 func TestParseExistingFile(t *testing.T) {
-	f, err := ioutil.TempFile("", "")
+	t.Parallel()
+	f, err := os.CreateTemp("", "")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -70,6 +74,7 @@ func TestParseExistingFile(t *testing.T) {
 }
 
 func TestParseTCPAddr(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.TCP()
 	err := p.value.Set("127.0.0.1:1234")
@@ -80,6 +85,7 @@ func TestParseTCPAddr(t *testing.T) {
 }
 
 func TestParseTCPAddrList(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	_ = p.TCPList()
 	err := p.value.Set("127.0.0.1:1234")
@@ -90,6 +96,7 @@ func TestParseTCPAddrList(t *testing.T) {
 }
 
 func TestFloat32(t *testing.T) {
+	t.Parallel()
 	p := parserMixin{}
 	v := p.Float32()
 	err := p.value.Set("123.45")
diff --git a/templates.go b/templates.go
index 703c2cd..05dd50b 100644
--- a/templates.go
+++ b/templates.go
@@ -47,7 +47,7 @@ Commands:
 {{end -}}
 `
 
-// Usage template where command's optional flags are listed separately
+// Usage template where command's optional flags are listed separately.
 var SeparateOptionalFlagsUsageTemplate = `{{define "FormatCommand" -}}
 {{if .FlagSummary}} {{.FlagSummary}}{{end -}}
 {{range .Args}}{{if not .Hidden}} {{if not .Required}}[{{end}}{{if .PlaceHolder}}{{.PlaceHolder}}{{else}}<{{.Name}}>{{end}}{{if .Value|IsCumulative}}...{{end}}{{if not .Required}}]{{end}}{{end}}{{end -}}
diff --git a/usage.go b/usage.go
index 9b3dd73..a8b0f2b 100644
--- a/usage.go
+++ b/usage.go
@@ -9,9 +9,7 @@ import (
 	"text/template"
 )
 
-var (
-	preIndent = "  "
-)
+var preIndent = "  "
 
 func formatTwoColumns(w io.Writer, indent, padding, width int, rows [][2]string) {
 	// Find size of first column.
@@ -104,8 +102,8 @@ type templateParseContext struct {
 
 type templateContext struct {
 	App     *ApplicationModel
-	Width   int
 	Context *templateParseContext
+	Width   int
 }
 
 // UsageForContext displays usage information from a ParseContext (obtained from
diff --git a/usage_test.go b/usage_test.go
index a438748..725e987 100644
--- a/usage_test.go
+++ b/usage_test.go
@@ -10,6 +10,7 @@ import (
 )
 
 func TestFormatTwoColumns(t *testing.T) {
+	t.Parallel()
 	buf := bytes.NewBuffer(nil)
 	formatTwoColumns(buf, 2, 2, 20, [][2]string{
 		{"--hello", "Hello world help with something that is cool."},
@@ -25,9 +26,11 @@ func TestFormatTwoColumns(t *testing.T) {
 }
 
 func TestFormatTwoColumnsWide(t *testing.T) {
+	t.Parallel()
 	samples := [][2]string{
 		{strings.Repeat("x", 29), "29 chars"},
-		{strings.Repeat("x", 30), "30 chars"}}
+		{strings.Repeat("x", 30), "30 chars"},
+	}
 	buf := bytes.NewBuffer(nil)
 	formatTwoColumns(buf, 0, 0, 200, samples)
 	expected := `xxxxxxxxxxxxxxxxxxxxxxxxxxxxx29 chars
@@ -38,6 +41,7 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 }
 
 func TestHiddenCommand(t *testing.T) {
+	t.Parallel()
 	templates := []struct{ name, template string }{
 		{"default", DefaultUsageTemplate},
 		{"Compact", CompactUsageTemplate},
@@ -66,6 +70,7 @@ func TestHiddenCommand(t *testing.T) {
 }
 
 func TestUsageFuncs(t *testing.T) {
+	t.Parallel()
 	var buf bytes.Buffer
 	a := New("test", "Test").Writer(&buf).Terminate(nil)
 	tpl := `{{ add 2 1 }}`
@@ -79,6 +84,7 @@ func TestUsageFuncs(t *testing.T) {
 }
 
 func TestCmdClause_HelpLong(t *testing.T) {
+	t.Parallel()
 	var buf bytes.Buffer
 	tpl := `{{define "FormatUsage"}}{{.HelpLong}}{{end -}}
 {{template "FormatUsage" .Context.SelectedCommand}}`
@@ -93,6 +99,7 @@ func TestCmdClause_HelpLong(t *testing.T) {
 }
 
 func TestArgEnvVar(t *testing.T) {
+	t.Parallel()
 	var buf bytes.Buffer
 
 	a := New("test", "Test").Writer(&buf).Terminate(nil)
diff --git a/values.go b/values.go
index e6e05bc..cb6bd82 100644
--- a/values.go
+++ b/values.go
@@ -87,9 +87,10 @@ type accumulator struct {
 // Use reflection to accumulate values into a slice.
 //
 // target := []string{}
-// newAccumulator(&target, func (value interface{}) Value {
-//   return newStringValue(value.(*string))
-// })
+//
+//	newAccumulator(&target, func (value interface{}) Value {
+//	  return newStringValue(value.(*string))
+//	})
 func newAccumulator(slice interface{}, element func(value interface{}) Value) *accumulator {
 	typ := reflect.TypeOf(slice)
 	if typ.Kind() != reflect.Ptr || typ.Elem().Kind() != reflect.Slice {
@@ -131,7 +132,7 @@ func (a *accumulator) IsCumulative() bool {
 
 func (b *boolValue) IsBoolFlag() bool { return true }
 
-// -- time.Duration Value
+// -- time.Duration Value.
 type durationValue time.Duration
 
 func newDurationValue(p *time.Duration) *durationValue {
@@ -148,7 +149,7 @@ func (d *durationValue) Get() interface{} { return time.Duration(*d) }
 
 func (d *durationValue) String() string { return (*time.Duration)(d).String() }
 
-// -- map[string]string Value
+// -- map[string]string Value.
 type stringMapValue map[string]string
 
 func newStringMapValue(p *map[string]string) *stringMapValue {
@@ -178,7 +179,7 @@ func (s *stringMapValue) IsCumulative() bool {
 	return true
 }
 
-// -- net.IP Value
+// -- net.IP Value.
 type ipValue net.IP
 
 func newIPValue(p *net.IP) *ipValue {
@@ -202,7 +203,7 @@ func (i *ipValue) String() string {
 	return (*net.IP)(i).String()
 }
 
-// -- *net.TCPAddr Value
+// -- *net.TCPAddr Value.
 type tcpAddrValue struct {
 	addr **net.TCPAddr
 }
@@ -294,7 +295,7 @@ func (f *fileValue) String() string {
 	return (*f.f).Name()
 }
 
-// -- url.URL Value
+// -- url.URL Value.
 type urlValue struct {
 	u **url.URL
 }
@@ -323,7 +324,7 @@ func (u *urlValue) String() string {
 	return (*u.u).String()
 }
 
-// -- []*url.URL Value
+// -- []*url.URL Value.
 type urlListValue []*url.URL
 
 func newURLListValue(p *[]*url.URL) *urlListValue {
@@ -386,7 +387,7 @@ func (e *enumValue) Get() interface{} {
 	return (string)(*e.value)
 }
 
-// -- []string Enum Value
+// -- []string Enum Value.
 type enumsValue struct {
 	value   *[]string
 	options []string
@@ -421,7 +422,7 @@ func (s *enumsValue) IsCumulative() bool {
 	return true
 }
 
-// -- units.Base2Bytes Value
+// -- units.Base2Bytes Value.
 type bytesValue units.Base2Bytes
 
 func newBytesValue(p *units.Base2Bytes) *bytesValue {
diff --git a/values_generated.go b/values_generated.go
index 8d492bf..a8a2704 100644
--- a/values_generated.go
+++ b/values_generated.go
@@ -11,7 +11,7 @@ import (
 
 // This file is autogenerated by "go generate .". Do not modify.
 
-// -- bool Value
+// -- bool Value.
 type boolValue struct{ v *bool }
 
 func newBoolValue(p *bool) *boolValue {
@@ -54,7 +54,7 @@ func (p *parserMixin) BoolListVar(target *[]bool) {
 	}))
 }
 
-// -- string Value
+// -- string Value.
 type stringValue struct{ v *string }
 
 func newStringValue(p *string) *stringValue {
@@ -97,7 +97,7 @@ func (p *parserMixin) StringsVar(target *[]string) {
 	}))
 }
 
-// -- uint Value
+// -- uint Value.
 type uintValue struct{ v *uint }
 
 func newUintValue(p *uint) *uintValue {
@@ -140,7 +140,7 @@ func (p *parserMixin) UintsVar(target *[]uint) {
 	}))
 }
 
-// -- uint8 Value
+// -- uint8 Value.
 type uint8Value struct{ v *uint8 }
 
 func newUint8Value(p *uint8) *uint8Value {
@@ -183,7 +183,7 @@ func (p *parserMixin) Uint8ListVar(target *[]uint8) {
 	}))
 }
 
-// -- uint16 Value
+// -- uint16 Value.
 type uint16Value struct{ v *uint16 }
 
 func newUint16Value(p *uint16) *uint16Value {
@@ -226,7 +226,7 @@ func (p *parserMixin) Uint16ListVar(target *[]uint16) {
 	}))
 }
 
-// -- uint32 Value
+// -- uint32 Value.
 type uint32Value struct{ v *uint32 }
 
 func newUint32Value(p *uint32) *uint32Value {
@@ -269,7 +269,7 @@ func (p *parserMixin) Uint32ListVar(target *[]uint32) {
 	}))
 }
 
-// -- uint64 Value
+// -- uint64 Value.
 type uint64Value struct{ v *uint64 }
 
 func newUint64Value(p *uint64) *uint64Value {
@@ -312,7 +312,7 @@ func (p *parserMixin) Uint64ListVar(target *[]uint64) {
 	}))
 }
 
-// -- int Value
+// -- int Value.
 type intValue struct{ v *int }
 
 func newIntValue(p *int) *intValue {
@@ -355,7 +355,7 @@ func (p *parserMixin) IntsVar(target *[]int) {
 	}))
 }
 
-// -- int8 Value
+// -- int8 Value.
 type int8Value struct{ v *int8 }
 
 func newInt8Value(p *int8) *int8Value {
@@ -398,7 +398,7 @@ func (p *parserMixin) Int8ListVar(target *[]int8) {
 	}))
 }
 
-// -- int16 Value
+// -- int16 Value.
 type int16Value struct{ v *int16 }
 
 func newInt16Value(p *int16) *int16Value {
@@ -441,7 +441,7 @@ func (p *parserMixin) Int16ListVar(target *[]int16) {
 	}))
 }
 
-// -- int32 Value
+// -- int32 Value.
 type int32Value struct{ v *int32 }
 
 func newInt32Value(p *int32) *int32Value {
@@ -484,7 +484,7 @@ func (p *parserMixin) Int32ListVar(target *[]int32) {
 	}))
 }
 
-// -- int64 Value
+// -- int64 Value.
 type int64Value struct{ v *int64 }
 
 func newInt64Value(p *int64) *int64Value {
@@ -527,7 +527,7 @@ func (p *parserMixin) Int64ListVar(target *[]int64) {
 	}))
 }
 
-// -- float64 Value
+// -- float64 Value.
 type float64Value struct{ v *float64 }
 
 func newFloat64Value(p *float64) *float64Value {
@@ -570,7 +570,7 @@ func (p *parserMixin) Float64ListVar(target *[]float64) {
 	}))
 }
 
-// -- float32 Value
+// -- float32 Value.
 type float32Value struct{ v *float32 }
 
 func newFloat32Value(p *float32) *float32Value {
@@ -691,7 +691,7 @@ func (p *parserMixin) ExistingFilesOrDirsVar(target *[]string) {
 	}))
 }
 
-// -- *regexp.Regexp Value
+// -- *regexp.Regexp Value.
 type regexpValue struct{ v **regexp.Regexp }
 
 func newRegexpValue(p **regexp.Regexp) *regexpValue {
@@ -734,7 +734,7 @@ func (p *parserMixin) RegexpListVar(target *[]*regexp.Regexp) {
 	}))
 }
 
-// -- net.IP Value
+// -- net.IP Value.
 type resolvedIPValue struct{ v *net.IP }
 
 func newResolvedIPValue(p *net.IP) *resolvedIPValue {
@@ -777,7 +777,7 @@ func (p *parserMixin) ResolvedIPListVar(target *[]net.IP) {
 	}))
 }
 
-// -- []byte Value
+// -- []byte Value.
 type hexBytesValue struct{ v *[]byte }
 
 func newHexBytesValue(p *[]byte) *hexBytesValue {
diff --git a/values_test.go b/values_test.go
index e16ee2a..043b37d 100644
--- a/values_test.go
+++ b/values_test.go
@@ -2,13 +2,13 @@ package kingpin
 
 import (
 	"net"
+	"testing"
 
 	"github.com/stretchr/testify/assert"
-
-	"testing"
 )
 
 func TestAccumulatorStrings(t *testing.T) {
+	t.Parallel()
 	target := []string{}
 	acc := newAccumulator(&target, func(v interface{}) Value { return newStringValue(v.(*string)) })
 	acc.Set("a")
@@ -18,6 +18,7 @@ func TestAccumulatorStrings(t *testing.T) {
 }
 
 func TestStrings(t *testing.T) {
+	t.Parallel()
 	app := New("", "")
 	app.Arg("a", "").Required().String()
 	app.Arg("b", "").Required().String()
@@ -27,6 +28,7 @@ func TestStrings(t *testing.T) {
 }
 
 func TestEnum(t *testing.T) {
+	t.Parallel()
 	app := New("", "")
 	a := app.Arg("a", "").Enum("one", "two", "three")
 	_, err := app.Parse([]string{"moo"})
@@ -37,6 +39,7 @@ func TestEnum(t *testing.T) {
 }
 
 func TestEnumVar(t *testing.T) {
+	t.Parallel()
 	app := New("", "")
 	var a string
 	app.Arg("a", "").EnumVar(&a, "one", "two", "three")
@@ -48,6 +51,7 @@ func TestEnumVar(t *testing.T) {
 }
 
 func TestCounter(t *testing.T) {
+	t.Parallel()
 	app := New("", "")
 	c := app.Flag("f", "").Counter()
 	_, err := app.Parse([]string{"--f", "--f", "--f"})
@@ -56,6 +60,7 @@ func TestCounter(t *testing.T) {
 }
 
 func TestIPv4Addr(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	flag := app.Flag("addr", "").ResolvedIP()
 	_, err := app.Parse([]string{"--addr", net.IPv4(1, 2, 3, 4).String()})
@@ -65,6 +70,7 @@ func TestIPv4Addr(t *testing.T) {
 }
 
 func TestInvalidIPv4Addr(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	app.Flag("addr", "").ResolvedIP()
 	_, err := app.Parse([]string{"--addr", "1.2.3.256"})
@@ -72,6 +78,7 @@ func TestInvalidIPv4Addr(t *testing.T) {
 }
 
 func TestIPv6Addr(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	flag := app.Flag("addr", "").ResolvedIP()
 	_, err := app.Parse([]string{"--addr", net.IPv6interfacelocalallnodes.String()})
@@ -81,6 +88,7 @@ func TestIPv6Addr(t *testing.T) {
 }
 
 func TestHexBytes(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	actual := app.Arg("bytes", "").HexBytes()
 	_, err := app.Parse([]string{"01020aff"})
@@ -89,6 +97,7 @@ func TestHexBytes(t *testing.T) {
 }
 
 func TestSetValueDoesNotReset(t *testing.T) {
+	t.Parallel()
 	app := newTestApp()
 	mapping := map[string]string{
 		"key": "value",