如何验证是否在Golang中调用了特定函数

Question

Currently I'm trying my hand at writing TDD in Go. I am however stuck at the following.

The test to write:

func TestFeatureStart(t *testing.T){

}

Implementation to test:

func (f *Feature) Start() error {
  cmd := exec.Command(f.Cmd)
  cmd.Start()
}

How would one test this simple bit. I figured I only wanted to verify that the exec-library is spoken to correctly. (The way I would in Java using Mockito). Can anyone help me write this test for I am not quite sure what the current available answers on the internet mean. They're suggesting the use of interfaces.

Currently the Feature-struct only contains a string Cmd.

Answer 1

You can fake the whole deal with interfaces, but you could also use fakeable functions. In the code:

var cmdStart = (*exec.Cmd).Start
func (f *Feature) Start() error {
    cmd := exec.Command(f.Cmd)
    return cmdStart(cmd)
}

In the tests:

called := false
cmdStart = func(*exec.Cmd) error { called = true; return nil }
f.Start()
if !called {
    t.Errorf("command didn't start")
}

See also: Andrew Gerrand's Testing Techniques talk.