Testing Pytest Fixtures

For test fixtures of much complexity (particularly ones intended to be shared and packaged as a plug-in), testing is essential. The short “Testing plugins” section of the “Writing plugins” chapter of the pytest manual is mostly adequate, but could be improved upon.

For example, it might be easier to understand failures of a fixture test by running it as a normal test, rather than through testdir.runpytest, so we might first just write a normal test:

import uuid as uuid

def test_uuid_pattern(uuid_pattern):
    """Test :func:`uuid_pattern`."""
    good_uuid = str(uuid.uuid1())
    assert uuid_pattern.match(good_uuid)

Now the fixture should be tested by running it with testdir.runpytest but rather than re-writing the test as a string for testdir.makepyfile, use the built-in inspect module to get the source of the test as a string with the getsource function:

import inspect

pytest_plugins = 'pytester'

def test_uuid_pattern_fixture(testdir):
    """Test :func:`uuid_pattern`."""
    result = testdir.runpytest('--verbose', plugins=['no:sugar'])
        '*::test_uuid_pattern PASSED',
    assert result.ret == 0

Note that I have expressly disabled the pytest-sugar plugin; because it changes the test report output, it messes up this test. It seems like it should be able to detect situations like this and disable itself but it does not. If pytest-sugar is not used, this can be elided. (A better solution might be to examine a structured report of the test run, such as the JUnit XML or --report-log=xxx, or perhaps use RunResult.assert_outcomes).