Reuse go logic and add tests

helpers.go

@@ -122,15 +122,6 @@ func asComment(c string) string {
 	removeNewlines := func(s string) string {
 		return strings.Replace(s, "\n", "\n// ", -1)
 	}
-	findLastIndex := func(rs []rune, r rune) int {
-		l := -1
-		for i, v := range rs {
-			if v == r {
-				l = i
-			}
-		}
-		return l
-	}
 	r := []rune(c)
 	for len(r) > 0 {
 		line := r
@@ -139,7 +130,9 @@ func asComment(c string) string {
 			break
 		}
 		line = line[:maxLen]
-		si := findLastIndex(line, []rune(" ")[0])
+		si := strings.LastIndexFunc(string(line), func(r rune) bool {
+			return unicode.IsSpace(r)
+		})
 		if si != -1 {
 			line = line[:si]
 		}

helpers_test.go

@@ -36,3 +36,38 @@ func TestInitialCap(t *testing.T) {
 		}
 	}
 }
+
+var asCommentTests = []struct {
+	Comment   string
+	Commented string
+}{
+	{
+		Comment: `This is a multi-line
+comment, it contains multiple
+lines.`,
+		Commented: `// This is a multi-line
+// comment, it contains multiple
+// lines.
+`,
+	},
+	{
+		Comment: `This is a fairly long comment line, it should be over seventy characters.`,
+		Commented: `// This is a fairly long comment line, it should be over seventy
+// characters.
+`,
+	},
+	{
+		Comment: `散りぬべき時知りてこそ世の中の花も花なれ人も人なれ`,
+		Commented: `// 散りぬべき時知りてこそ世の中の花も花なれ人も人なれ
+`,
+	},
+}
+
+func TestAsComment(t *testing.T) {
+	for i, act := range asCommentTests {
+		c := asComment(act.Comment)
+		if c != act.Commented {
+			t.Errorf("%d: wants %v+, got %v+", i, act.Commented, c)
+		}
+	}
+}