mantle/kola: add colors to highlight tests results

Removed the "Warn" parts from the cherry pick to make it compile
because we didn't backport the warn:true stuff here.

(cherry picked from commit a191716)

Author: nikita-dubrovskii

mantle/harness/harness.go

@@ -609,7 +609,7 @@ func (t *H) report() {
 
 	status := t.status()
 	if status == testresult.Fail || t.suite.opts.Verbose {
-		t.flushToParent(format, status, t.name, dstr)
+		t.flushToParent(format, status.Display(), t.name, dstr)
 	}
 
 	// TODO: store multiple buffers for subtests without indentation

mantle/harness/harness_test.go

@@ -76,6 +76,9 @@ func TestContextCancel(t *testing.T) {
 }
 
 func TestSubTests(t *testing.T) {
+	// When TERM is set, we add colors to highlight tests results: '--- FAIL' will be in red '--- \033[31mFAIL\033[0m'
+	// Let's unset it here for simplicity
+	os.Unsetenv("TERM")
 	realTest := t
 	testCases := []struct {
 		desc   string

mantle/harness/testresult/status.go

@@ -14,10 +14,31 @@
 
 package testresult
 
+import "os"
+
 const (
 	Fail TestResult = "FAIL"
 	Skip TestResult = "SKIP"
 	Pass TestResult = "PASS"
 )
 
 type TestResult string
+
+func (s TestResult) Display() string {
+	if term, has_term := os.LookupEnv("TERM"); !has_term || term == "" {
+		return string(s)
+	}
+
+	red := "\033[31m"
+	blue := "\033[34m"
+	green := "\033[32m"
+	reset := "\033[0m"
+
+	if s == Fail {
+		return red + string(s) + reset
+	} else if s == Skip {
+		return blue + string(s) + reset
+	} else {
+		return green + string(s) + reset
+	}
+}