Golang test stdout

Question

I am trying to test some functions that print ANSI escape codes. e.g.

// Print a line in a color
func PrintlnColor(color string, a ...interface{}) {
    fmt.Print("\x1b[31m")
    fmt.Print(a...)
    fmt.Println("\x1b[0m")
}

I tried using Examples to do it, but they don't seem to like escape codes.

Is there any way to test what is written to stdout?

Answer 1

Using fmt.Fprint to print to io.Writer lets you control where the output is written.

var out io.Writer = os.Stdout

func main() {
    // write to Stdout
    PrintlnColor("foo")

    buf := &bytes.Buffer{}
    out = buf

    // write  to buffer
    PrintlnColor("foo")

    fmt.Println(buf.String())
}

// Print a line in a color
func PrintlnColor(a ...interface{}) {
    fmt.Fprint(out, "\x1b[31m")
    fmt.Fprint(out, a...)
    fmt.Fprintln(out, "\x1b[0m")
}

Go play