05 PyTest Mark and Parameterize

Mark¶

• Marking in pytest allows you to add metadata to your test functions, such as categorizing tests or marking them with certain properties like 'slow' or 'fast'.

Marks are needed when:

1. Selective Testing: You want to run a subset of tests based on certain criteria, such as all 'slow' tests or all 'integration' tests. (like tag)
2. Conditionally Skipping Tests: You need to skip tests under certain conditions, such as missing dependencies or an unsupported platform.
3. Expected Failures: You want to mark tests that are known to fail, possibly due to a known bug that hasn't been fixed yet.

Add tag to test function¶

• add slow tag to the test_very_slow() function

@pytest.mark.slow
def test_very_slow():
    time.sleep(5)
    assert calc.add(10,5) == 15

Filter by tag and run test¶

• pytest -m slow
  • only run test that tag as slow

Skip test¶

1. Add skip tag to function

@pytest.mark.skip(reason="This feature is currently broken")
def test_add():
    assert calc.add(10,5) == 14

2. pytest will automatically ignore this function

Mark those fails we already know¶

1. Add xfail tag to those functions

@pytest.mark.xfail(reason="We know this gonna fail")
def test_divide_zero():
    assert calc.divide(10,5)

2. Result will use X to show these fails

Parameterization¶

Parameterization in pytest is a powerful feature used for running a test function multiple times with different sets of arguments.

• It's also a mark in pytest

Parameterization is needed when:

1. Testing Various Input Sets: You have a function that should work correctly with various inputs, and you want to test all these cases without writing separate test functions for each input set.
2. Cross-Browser or Cross-Platform Testing: You want to run the same tests across multiple environments, such as different browsers or operating systems.
3. Boundary Value Testing: When you want to test edge cases or boundary values for a function, parameterization allows you to easily define these boundary values as parameters.

Example¶

• We want to test the area() function of Square class

class Rectangle(Shape):
    def __init__(self,length,width) -> None:
        self.length = length
        self.width = width

    def area(self):
        return self.length * self.width

    def perimeter(self):
        return 2 * (self.length + self.width)

    def __eq__(self, other: object) -> bool:
        if not isinstance(other,Rectangle):
            return False
        return self.width == other.width and self.length == self.length

class Square(Rectangle):
    def __init__(self, side_length) -> None:
        super().__init__(side_length, side_length)

2. use pytest.mark.parameterize("params",[args]) to tag the test function

@pytest.mark.parametrize("side_length, expected_area",[(5,25),(4,16),(9,81)])
def test_multiple_square_areas(side_length, expected_area):
    assert shapes.Square(side_length).area() == expected_area

3. Show result