Does Python provide support for Assumptions as pre-conditions?

Question

Assumptions in Python unit tests

Does Python provide support for Assumptions to be used as pre-conditions for tests similar to those provided by JUnit with assumeThat(...) methods for Java.

This is important, because of the application of Hoare Logic, to quote JUnit:

A set of methods useful for stating assumptions about the conditions in which a test is meaningful. A failed assumption does not mean the code is broken, but that the test provides no useful information. Assume basically means "don't run this test if these conditions don't apply". The default JUnit runner skips tests with failing assumptions. Custom runners may behave differently.

It seems that Python doesn't provide these out of the box in its unittest framework. I've tentatively POC my own approach by extending unittest.TestCase.

class LoggingTestCase(unittest.TestCase):
    def assumeTrue(self, expr: Any, msg: Any = ...) -> None:
        try:
            super().assertTrue(expr, msg)
            self.test_result = TestResult.PASSED
        except AssertionError as e:
            self.test_result = TestResult.SKIPPED
            raise InvalidAssumption(e)

With this unittest of behaviour:

class TestLoggingTestCase(LoggingTestCase):
    def test_assumeTrue(self):
        self.assertRaises(InvalidAssumption, self.assumeTrue, False)  # Passes as expected.
        self.assertRaises(InvalidAssumption, self.assumeTrue, True)  # Fails as expected.

This approach seems to exhibit the correct behaviour I want, is this the best approach, is there better way to do this, or 3rd party library to use? I'm looking for a better way than wrapping all the base assertions this way to make my own assumptions.

Answer 1

I use pytest skipif for this purpose.

http://doc.pytest.org/en/latest/skipping.html