diff --git a/pkg/commands/compute/metadata_test.go b/pkg/commands/compute/metadata_test.go
index dd276a5a9..d3ac994cb 100644
--- a/pkg/commands/compute/metadata_test.go
+++ b/pkg/commands/compute/metadata_test.go
@@ -1,7 +1,6 @@
 package compute_test
 
 import (
-	"bytes"
 	"os"
 	"path/filepath"
 	"testing"
@@ -13,6 +12,7 @@ import (
 	"github.com/fastly/cli/pkg/global"
 	"github.com/fastly/cli/pkg/revision"
 	"github.com/fastly/cli/pkg/testutil"
+	"github.com/fastly/cli/pkg/threadsafe"
 )
 
 func TestMetadata(t *testing.T) {
@@ -47,7 +47,7 @@ func TestMetadata(t *testing.T) {
 				},
 			},
 			WantOutput: "SUCCESS: configuration updated",
-			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ bytes.Buffer) {
+			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ *threadsafe.Buffer) {
 				data, err := os.ReadFile(opts.ConfigPath)
 				if err != nil {
 					t.Error(err)
@@ -80,7 +80,7 @@ func TestMetadata(t *testing.T) {
 				},
 			},
 			WantOutput: "SUCCESS: configuration updated",
-			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ bytes.Buffer) {
+			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ *threadsafe.Buffer) {
 				data, err := os.ReadFile(opts.ConfigPath)
 				if err != nil {
 					t.Error(err)
@@ -116,7 +116,7 @@ func TestMetadata(t *testing.T) {
 				"INFO: We will enable all metadata except for the specified `--disable-*` flags",
 				"SUCCESS: configuration updated",
 			},
-			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ bytes.Buffer) {
+			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ *threadsafe.Buffer) {
 				data, err := os.ReadFile(opts.ConfigPath)
 				if err != nil {
 					t.Error(err)
@@ -152,7 +152,7 @@ func TestMetadata(t *testing.T) {
 				"INFO: We will disable all metadata except for the specified `--enable-*` flags",
 				"SUCCESS: configuration updated",
 			},
-			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ bytes.Buffer) {
+			Validator: func(t *testing.T, _ *testutil.TestScenario, opts *global.Data, _ *threadsafe.Buffer) {
 				data, err := os.ReadFile(opts.ConfigPath)
 				if err != nil {
 					t.Error(err)
diff --git a/pkg/commands/sso/sso_test.go b/pkg/commands/sso/sso_test.go
index aa9bb82cf..2d9a66953 100644
--- a/pkg/commands/sso/sso_test.go
+++ b/pkg/commands/sso/sso_test.go
@@ -1,7 +1,6 @@
 package sso_test
 
 import (
-	"bytes"
 	"errors"
 	"testing"
 	"time"
@@ -13,6 +12,7 @@ import (
 	"github.com/fastly/cli/pkg/global"
 	"github.com/fastly/cli/pkg/mock"
 	"github.com/fastly/cli/pkg/testutil"
+	"github.com/fastly/cli/pkg/threadsafe"
 )
 
 func TestSSO(t *testing.T) {
@@ -99,7 +99,7 @@ func TestSSO(t *testing.T) {
 				"We need to open your browser to authenticate you.",
 				"Session token (persisted to your local configuration): 123",
 			},
-			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout bytes.Buffer) {
+			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout *threadsafe.Buffer) {
 				const expectedToken = "123"
 				userProfile := opts.Config.Profiles["user"]
 				if userProfile.Token != expectedToken {
@@ -139,7 +139,7 @@ func TestSSO(t *testing.T) {
 				"We need to open your browser to authenticate you.",
 				"Session token (persisted to your local configuration): 123",
 			},
-			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout bytes.Buffer) {
+			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout *threadsafe.Buffer) {
 				const expectedToken = "123"
 				userProfile := opts.Config.Profiles["test_user"]
 				if userProfile.Token != expectedToken {
@@ -191,7 +191,7 @@ func TestSSO(t *testing.T) {
 				// "is not a Fastly SSO (Single Sign-On) generated token",
 				"{Latitude:1 Longtitude:2 X:3 Y:4}",
 			},
-			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout bytes.Buffer) {
+			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout *threadsafe.Buffer) {
 				const expectedToken = "mock-token"
 				userProfile := opts.Config.Profiles["user"]
 				if userProfile.Token != expectedToken {
@@ -221,7 +221,7 @@ func TestSSO(t *testing.T) {
 			},
 			WantOutput:     "Your access token has expired and so has your refresh token.",
 			DontWantOutput: "{Latitude:1 Longtitude:2 X:3 Y:4}",
-			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout bytes.Buffer) {
+			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout *threadsafe.Buffer) {
 				const expectedToken = "mock-token"
 				userProfile := opts.Config.Profiles["user"]
 				if userProfile.Token != expectedToken {
@@ -283,7 +283,7 @@ func TestSSO(t *testing.T) {
 				"Session token (persisted to your local configuration): 123",
 				"{Latitude:1 Longtitude:2 X:3 Y:4}",
 			},
-			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout bytes.Buffer) {
+			Validator: func(t *testing.T, scenario *testutil.TestScenario, opts *global.Data, stdout *threadsafe.Buffer) {
 				const expectedToken = "123"
 				userProfile := opts.Config.Profiles["user"]
 				if userProfile.Token != expectedToken {
diff --git a/pkg/testutil/scenarios.go b/pkg/testutil/scenarios.go
index 4504ffe27..1a2c08460 100644
--- a/pkg/testutil/scenarios.go
+++ b/pkg/testutil/scenarios.go
@@ -1,12 +1,12 @@
 package testutil
 
 import (
-	"bytes"
 	"fmt"
 	"github.com/fastly/cli/pkg/app"
 	"github.com/fastly/cli/pkg/config"
 	"github.com/fastly/cli/pkg/global"
 	"github.com/fastly/cli/pkg/mock"
+	"github.com/fastly/cli/pkg/threadsafe"
 	"io"
 	"os"
 	"slices"
@@ -54,7 +54,7 @@ type TestScenario struct {
 	Stdin []string
 	// Validator function can perform additional validation on the results
 	// of the scenario
-	Validator func(t *testing.T, scenario *TestScenario, opts *global.Data, stdout bytes.Buffer)
+	Validator func(t *testing.T, scenario *TestScenario, opts *global.Data, stdout *threadsafe.Buffer)
 	// WantError will cause the scenario to fail if this string
 	// does not appear in an Error
 	WantError string
@@ -95,7 +95,7 @@ func RunScenario(t *testing.T, command []string, scenario TestScenario) {
 			err      error
 			fullargs []string
 			rootdir  string
-			stdout   bytes.Buffer
+			stdout   threadsafe.Buffer
 		)
 
 		if len(scenario.Arg) > 0 {
@@ -233,7 +233,7 @@ func RunScenario(t *testing.T, command []string, scenario TestScenario) {
 		}
 
 		if scenario.Validator != nil {
-			scenario.Validator(t, &scenario, opts, stdout)
+			scenario.Validator(t, &scenario, opts, &stdout)
 		}
 	})
 }