Golang: testing terminal output

When working with Go, we always strive to test, one thing we want to test, is the terminal output, this is a simple way for testing the standard output.

Testing the terminal output

// save copy of std out
old := os.Stdout
//create read and write pupe
r, w, _ := os.Pipe()
// set the stdout to the pipe
os.Stdout = w
// we excute the function
someFunctionCall()
// close the resource
w.Close()
// reset the stdout back to the orignal
os.Stdout = old
// read from the read pipe we create
got, _ := io.ReadAll(r)
// check if out is what you want
// want := something you want
//if got != want {
    // throw an error.
//}

Example

SayHello function

Given we have this example function, saying Hello World!, and we want to test this out, whether the terminal is properly printing it out.

func sayHello() {
    fmt.Printf("Hello World!")
}

The test we function

To test we apply the same method, and we test for strings equality.

func Test_SayHello(t *testing.T) {
    // save copy of std out
    old := os.Stdout
    //create read and write pupe
    r, w, _ := os.Pipe()
    // set the stdout to the pipe
    os.Stdout = w
    // we excuted
    sayHello()
    // close the resource
    w.Close()
    // reset the stdout back to the orignal
    os.Stdout = old
    // read from the read output we create
    out, _ := io.ReadAll(r)
    // convert to string
    got := string(out)
    // what we expect
    want := "Hello World!"
    if strings.Compare(got, want) != 0 {
        t.Errorf("incorrect hello got: %v", string(out))
    }
    if got != want {
        t.Errorf("incorrect hello got: %v", string(out))
    }
}