Better coloring performance

This allows the compiler to inline the ANSI codes
and to save 2 bytes/op, reduucing the perf at 7 bytes/op
instead of 9 bytes/op. Knowing that the original code only
uses 3 bytes/op, there is still space for improvement

Author: EwenQuim

assert/colors.go

@@ -7,22 +7,24 @@ import (
 	"golang.org/x/term"
 )
 
-const redMark = "\033[0;31m"
-const greenMark = "\033[0;32m"
-const endMark = "\033[0m"
+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 redMark + fmt.Sprintf("%s", i) + endMark
+		return fmt.Sprintf(redMark+"%s"+endMark, i)
 	}
 	return i
 }
 
 func greenColored(i interface{}) interface{} {
 	if isTerminal {
-		return greenMark + fmt.Sprintf("%s", i) + endMark
+		return fmt.Sprintf(greenMark+"%s"+endMark, i)
 	}
 	return i
 }
-
-var isTerminal = term.IsTerminal(int(os.Stdout.Fd()))

assert/colors_test.go

@@ -1,6 +1,9 @@
 package assert
 
-import "testing"
+import (
+	"fmt"
+	"testing"
+)
 
 func BenchmarkColored(b *testing.B) {
 	b.Run("benchMarkingString", func(b *testing.B) {
@@ -18,3 +21,33 @@ func BenchmarkColored(b *testing.B) {
 		}
 	})
 }
+
+// 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), "")
+		}
+	})
+
+}