Unit testing with the pytest module

The pytest tool allows us to step beyond the examples used by doctest. Instead of using a subclass of unittest.TestCase, the pytest tool lets us use function definitions. The pytest approach uses Python's built-in assert statement, leaving the test case looking somewhat simpler. The pytest test design avoids using the complex mix of assertion methods.

The pytest tool is not part of Python; it needs to be installed separately. Use a command like this:

python -m pip install pytest

In this recipe, we'll look at how we can use pytest to simplify our test cases.

Getting ready

The ideas behind the Gherkin language can help to structure a test. In this test specification language, each scenario is described by GIVEN-WHEN-THEN steps. For this recipe, we have a scenario like this:

Scenario: Summary object can add values and compute statistics.
  Given a Summary object
  And numbers in the range 0 to 1000 (inclusive...