运行测试时如何丢弃打印输出

Question

Using Go 1.11 I have a function that prints a label above a user input. This is fine and works but when I have started to write the test for this function it prints out this label when running the tests.

I have also use log.Print but then in the test file adding the following

func init() {
  log.SetOutput(ioutil.Discard)
}

This stops the log.Print from being displayed when running the tests. So how do I get it to do the same for any fmt.Println?

UPDATE

I thought I would post the func that I am testing and how I set up,

func checkLoop(loopCount int) int {
  var input int
  var ok bool

  for !ok {
    fmt.Printf("Input %d  ::  ", loopCount)
    ok, input = takeInput()
  }

  return input
}

So takeInput() only takes the users input, using fmt.Scan and checks it to see if its within a set range I want. So it returns a bool and if its false it will re-use the label to check what input number it is.

Answer 1

For example,

discard_test.go:

package main

import (
    "fmt"
    "os"
    "syscall"
    "testing"
)

func printLabel(label string) {
    fmt.Println(label)
}

func TestDiscardLabel(t *testing.T) {
    defer func(stdout *os.File) {
        os.Stdout = stdout
    }(os.Stdout)
    os.Stdout = os.NewFile(uintptr(syscall.Stdin), os.DevNull)
    printLabel("Discard:")
}

func TestPrintLabel(t *testing.T) {
    printLabel("Print:")
}

Output:

$ go test discard_test.go -v
--- PASS: TestDiscardLabel (0.00s)
=== RUN   TestPrintLabel
Print:
--- PASS: TestPrintLabel (0.00s)
PASS
$