How to test a function’s output (stdout/stderr) in unit tests

One thing to also remember, there’s nothing stopping you from writing functions to avoid the boilerplate.

For example I have a command line app that uses log and I wrote this function:

func captureOutput(f func()) string {
    var buf bytes.Buffer
    log.SetOutput(&buf)
    f()
    log.SetOutput(os.Stderr)
    return buf.String()
}

Then used it like this:

output := captureOutput(func() {
    client.RemoveCertificate("www.example.com")
})
assert.Equal(t, "removed certificate www.example.com\n", output)

Using this assert library: http://godoc.org/github.com/stretchr/testify/assert.