Mok — thread-safe mocking library for Golang

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Jonathan Hall came up with a very interesting idea on how to mock interfaces without using of third-party libraries. This approach can be briefly described as follows:

// Mock of the io.Reader interface.
type ReaderMock struct {
 ReadFunc func(p []byte) (n int, err error)
}
 
func (m *ReaderMock) Read(p []byte) (n int, err error) {
 return m.ReadFunc(p) // Here we use only one function for each method call.
}

Looks very nice and simple! However, when testing cmd-stream, it turned out that it is much more convenient to use a separate function for each method call, as well as to have multithreading support. This is how mok was born. Just a small example of how to use it:

  // Here we register several calls to the Read() method, and then call it
  // several times as well. Each method call is just a function.
  // If we want to register one function several times, we can use the
  // RegisterN() method. This is especially useful when testing concurrent 
  // method invocations.
  var (
    reader = NewReaderMock().RegisterRead(func(p []byte) (n int, err error) {
      p[0] = 1
      return 1, nil
    }).RegisterRead(func(p []byte) (n int, err error) {
      p[0] = 2
      p[1] = 2
      return 2, nil
    }).RegisterNRead(2, func(p []byte) (n int, err error) {
      return 0, io.EOF
    })
    b = make([]byte, 2)
  )
  // In total, we have registered 4 calls to the Read() method.

  // First call.
  n, _ := reader.Read(b)
  // We expect to read 1 byte.
  assert.Equal(n, 1, t)
 // ...

More details can be found at github.