Christoph Gockel

To mock or not to mock

10 Jul 2014

Part of the feedback I got in this week’s iteration meeting with Jim was to clean up the specs for my Game class.

I am not particular happy the way the specs looked like either. For my taste there is too much stubbing and mocking going with no real concept visible.

So, today I started working on adding more expressiveness to the specs for a while. They’re not quite in the shape I want them to be, but I think it’s at least a small improvement compared to the initial version.

It’s just that they’re still not as readable as other tests that you see in other RSpec examples. Will work further on that tomorrow.

Maybe part of the problem is the nature of the Game class itself. It has the most collaborators of all classes in the game. It is responsible for the correct sequence of the game itself. Asking the players for moves, placing their moves on the board, switching players, redo. All that until there’s a winner or a draw.

And as I want to focus on the logic/behaviour inside Game’s methods, I inject most of the collaborators as test doubles. And these test doubles need to be properly set up before a test. That lead quickly to a lot of set up code scattered throughout the test class.

Another thing is that some test doubles are used as spies, some as mocks. As a first approach I started to change the mocks to spies. Mostly because I don’t neccessarily like that the use of a mock changes the order of the Arrange, Act, Assert Pattern.

Take the following spec for example:

  it 'displays the board content for each round plus at the end of a game' do
    expect(display).to receive(:show_contents).with(board).exactly(4).times

It sets a mock-expectation on the test double display that method .show_contents() should be called exactly four times.

In contrast, this is the same spec using a spy:

  it 'displays the board content for each round plus at the end of a game' do
    expect(display).to have_received(:show_contents).exactly(4).times

Ignoring prepare_two_rounds_game for the moment, what stands out the most, is that the actual expectation comes after the production code has been executed.

For me this feels more natural. But maybe it’s just because I’m more used to have (manual) verifications at the end of a test case.