Colorizing test output

assert/assertions.go

@@ -421,7 +421,7 @@ func Equal(t TestingT, expected, actual interface{}, msgAndArgs ...interface{})
 		expected, actual = formatUnequalValues(expected, actual)
 		return Fail(t, fmt.Sprintf("Not equal: \n"+
 			"expected: %s\n"+
-			"actual  : %s%s", expected, actual, diff), msgAndArgs...)
+			"actual  : %s%s", greenColored(expected), redColored(actual), diff), msgAndArgs...)
 	}
 
 	return true

assert/colors.go

@@ -0,0 +1,30 @@
+package assert
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/term"
+)
+
+const (
+	redMark   = "\033[0;31m"
+	greenMark = "\033[0;32m"
+	endMark   = "\033[0m"
+)
+
+var isTerminal = term.IsTerminal(int(os.Stdout.Fd()))
+
+func redColored(i interface{}) interface{} {
+	if isTerminal {
+		return fmt.Sprintf(redMark+"%s"+endMark, i)
+	}
+	return i
+}
+
+func greenColored(i interface{}) interface{} {
+	if isTerminal {
+		return fmt.Sprintf(greenMark+"%s"+endMark, i)
+	}
+	return i
+}

assert/colors_test.go

@@ -0,0 +1,53 @@
+package assert
+
+import (
+	"fmt"
+	"testing"
+)
+
+func BenchmarkColored(b *testing.B) {
+	b.Run("benchMarkingString", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			greenColored("helloWorld")
+		}
+	})
+	b.Run("benchMarkingStruct", func(b *testing.B) {
+		s := struct {
+			a int
+			b string
+		}{3, "helloWorld"}
+		for i := 0; i < b.N; i++ {
+			greenColored(s)
+		}
+	})
+}
+
+// Not benchmarking `Equal` but the string formatting
+// because it will make the benchmark fail.
+func BenchmarkEqual(b *testing.B) {
+
+	s := struct {
+		a int
+		b string
+	}{3, "helloWorld"}
+
+	b.Run("Base", func(b *testing.B) {
+
+		for i := 0; i < b.N; i++ {
+			_ = fmt.Sprintf("Not equal: \n"+
+				"expected: %v\n"+
+				"actual  : %v%s", s, s, "")
+		}
+	})
+
+	b.Run("Colored (test with and without terminal)", func(b *testing.B) {
+		// This benchmark give very different results whether the output is a terminal or not.
+
+		for i := 0; i < b.N; i++ {
+			_ = fmt.Sprintf("Not equal: \n"+
+				"expected: %s\n"+
+				"actual  : %s%s", greenColored(s), redColored(s), "")
+		}
+	})
+
+}

go.mod

@@ -8,5 +8,8 @@ require (
 	github.com/davecgh/go-spew v1.1.1
 	github.com/pmezard/go-difflib v1.0.0
 	github.com/stretchr/objx v0.5.0
+	golang.org/x/term v0.12.0
 	gopkg.in/yaml.v3 v3.0.1
 )
+
+require golang.org/x/sys v0.12.0 // indirect

go.sum

@@ -9,6 +9,10 @@ github.com/stretchr/objx v0.5.0 h1:1zr/of2m5FGMsad5YfcqgdqdWrIhu+EBEJRhR1U7z/c=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
 github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
+golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.12.0 h1:/ZfYdc3zq+q02Rv9vGqTeSItdzZTSNDmfTi0mBAuidU=
+golang.org/x/term v0.12.0/go.mod h1:owVbMEjm3cBLCHdkQu9b1opXd4ETQWc3BhuQGKgXgvU=
 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=