Add the LevelEnablerFunc and test case (#208)

* add the levelenablerfunc for #201

* add the test for levelenablerfunc #205

* remove the comment in test and change code into the buf.Line()

level.go

@@ -72,6 +72,16 @@ const (
 	FatalLevel
 )
 
+// LevelEnablerFunc is a convenient way to implement LevelEnabler around an
+// anonymous function. It is also a valid Option to pass to a logger.
+type LevelEnablerFunc func(Level) bool
+
+// This allows an LevelEnablerFunc to be used as an option.
+func (f LevelEnablerFunc) apply(m *Meta) { m.LevelEnabler = f }
+
+// Enabled calls the wrapped function.
+func (f LevelEnablerFunc) Enabled(lvl Level) bool { return f(lvl) }
+
 // String returns a lower-case ASCII representation of the log level.
 func (l Level) String() string {
 	switch l {

level_test.go

@@ -26,6 +26,17 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+func TestLevelEnablerFunc(t *testing.T) {
+	opts := []Option{Fields(Int("foo", 42)), LevelEnablerFunc(func(l Level) bool { return l == DebugLevel })}
+	withJSONLogger(t, opts, func(log Logger, buf *testBuffer) {
+		log.Debug("@debug", Int("logger", 0))
+		log.Info("@info", Int("logger", 0))
+		assert.Equal(t, []string{
+			`{"level":"debug","msg":"@debug","foo":42,"logger":0}`,
+		}, buf.Lines())
+	})
+}
+
 func TestLevelString(t *testing.T) {
 	tests := map[Level]string{
 		DebugLevel:  "debug",