TestMigration setUpClass

[eagmon]

Create TestMigration setUpClass method suggested by @1fish2 in #91. This allows us to load sim_data only once for all the migration tests, and saves pytest a lot of time.

[1fish2]

Oh. Can this use the normal pytest runner?

The test framework has features to make testing easier including discovering the test cases so you needn't build a collection of them, an annotation to skip a specific test, CLI args to run all or specific tests or named tests or start with the tests that failed last time, and setUp/tearDown methods.

class TestMigration:
    sim_data = None

    @classmethod
    def setUpClass(cls):
        self.sim_data = LoadSimData(sim_data_path=SIM_DATA_PATH, seed=0)

    @classmethod
    def tearDownClass(cls):
        self.sim_data = None  # not really needed

    def test_metabolism_migration():
        config = self.sim_data.get_metabolism_config()
        ...

    # ...

If for some reason you need test functions instead of test classes, I think setUpModule() handles setup work for a source file's test functions.

One can create modular pytest fixtures so test methods can easily ask for inputs, ways to run a test on a collection of inputs, capture python warnings, and more. There are also pre-provided fixtures that do things like capture stdout and stderr, parameterize test cases, cache values across pytest runs, make a tempdir, temporarily monkey-patch something.

I haven't yet used fixtures but I think using them for data injection looks like this:

import pytest

_sim_data = None

@pytest.fixture
def sim_data():
    if _sim_data is None:
        _sim_data = LoadSimData(sim_data_path=SIM_DATA_PATH, seed=0)
    return _sim_data

def test_metabolism_migration(sim_data):
    config = sim_data.get_metabolism_config()
    ...

def test_something_else(sim_data):
    ...

and the fixture could be in one module and used in all the others. That'd only load sim_data once. If need be, the fixture could do a deepcopy() of the sim_data each time. That'd be a lot faster than reloading a pickle file, while insulating the tests from any other tests that mutate sim_data.

[1fish2]

I forgot the self arg for def test_metabolism_migration(self).

It looks like we can use Python style names setup_class(cls) and teardown_class(cls) in place of the Java-style names setUpClass(cls) in Python's built-in unittest library. With unittest, I think a test class has to subclass unittest.TestCase, and that might be needed to use setUpClass(cls) et al. Unittest does ordinary OOP. pytest does lots of reflection to save boilerplate.