Simplify the _get_default_display_method tests using unittest.mock

[seisman]

Refer to pytest-dev/pytest#4576 (comment) for comparisons of pytest.monkeypatch, unittest.mock and pytest-mock.

unittest.mock provides more features than pytest.monkeypatch which can simplify our tests. For example, with mock.call_count, we can directly count how many times a function/method is called, rather than implementing our own counter (like what're doing in

pygmt/pygmt/tests/test_clib_loading.py

Line 224 in d1ab97c

def _mock_ctypes_cdll_return(self, libname): # noqa: ARG002

).

Personally, I prefer pytest-mock which is as powerful as unittest.mock and can be used as a fixture, while unittest.mock must be used as a context manager or a decorator.

I think we have many options:

1. pytest.monkeypatch only, which means in some cases, we have to write more codes for tests
2. unittest.mock only or pytest-mock only
3. pytest.monkeypatch + unittest.mock
4. pytest.monkeypatch + pytest-mock

[weiji14]

Haven't played around with unittest.mock much yet, but does this unittest.mock.path call need to be here on top as a decorator, rather than in the test function below? I find this looks a little unintuitive (even though it is less code) compared to setting up the MockIPython class inside the unit test which makes it clear what is happening.

[seisman]

Here are different ways to mock IPython:

1. Define a custom class, as in the current main branch and use pytest.monkeypatch

class MockIPython:
    def __init__(self):
        self.config = {"IPKernelApp": True}

    # Mock IPython.get_ipython() to return a MockIPython instance.
    mock_ipython = MockIPython()
    monkeypatch.setattr(IPython, "get_ipython", lambda: mock_ipython)

2. Use mock/patch as a decorator

@patch("IPython.get_ipython", return_value=Mock(config={"IPKernelApp": True}))
def test_xxxx():
    ...

3. Use mock/patch as a context manager

def test_xxxx():
    with patch("IPython.get_ipython", return_value=Mock(config={"IPKernelApp": True})):
        ....

Maybe we should use option 3 although it means more indentations?

[weiji14]

Yes, option 3 sounds good.

[seisman]

OK, I've changed it to context manager in d08001c.