Writing Tests

Python Tests

• To allow use of deprecated methods in Python tests, use the decorator:

  @pytest.mark.usefixtures("allow_deprecated")
  

Transition from unittest to pytest

Starting in Cantera 2.6, we transitioned from using the built-in unittest module to run Cantera’s Python test suite to using the pytest framework. However, many of the existing tests are still written in the unittest style (which is also supported by pytest). The following recommendations apply to new tests and tests that are being significantly modified:

• Use pytest-style asserts instead of unittest member functions like assertWhatever. Examples:

  assert 0 <= idom < len(self.domains)
  assert gas.n_species == N + 1
  assert "X_H2" in header.split(",")
  

• Use pytest.approx in preference to assertAlmostEqual. Add from pytest import approx to any test file that doesn’t already contain it. Examples:

  assert q1.T == approx(T1)  # scalar
  assert sl_mole == approx(sl_mass, rel=0.1)  # specific relative tolerance
  assert list(jet.X[k, :]) == approx(list(self.sim.X[k, :]), tol_X)  # arrays
  assert X == approx([0.07748481, 0.048165072, 0.01446654])
  

• Use with pytest.raises instead of unittest’s method of handling “assert raises”. Example:

  with pytest.raises(ct.CanteraError, match="No component named 'spam'"):
      self.r1.set_advance_limit("spam", 0.1)