Test Discovery Rules

How pytest Finds Tests

One of pytest's best features is automatic test discovery. You do not need to register tests manually. pytest searches your project for files, classes, and functions that match specific naming conventions.

File Discovery

By default, pytest collects test files that match these patterns:

test_*.py    # Files starting with test_
*_test.py    # Files ending with _test

Any Python file with one of these names will be scanned for test functions and classes.

Function Discovery

Inside test files, pytest looks for functions and methods that start with test_:

# This WILL be collected as a test
def test_login():
    assert True

# This will NOT be collected
def login():
    assert True

# Helper functions should not start with test_
def helper_function():
    return 42

Class Discovery

pytest also collects test classes. Classes must start with Test and contain methods that start with test_:

class TestCalculator:  # Collected
    def test_add(self):
        assert 1 + 1 == 2

    def helper(self):  # NOT collected (no test_ prefix)
        pass

class calculator:  # NOT collected (does not start with Test)
    def test_add(self):
        assert 1 + 1 == 2

Customizing Discovery

You can override the default patterns in pytest.ini:

[pytest]
python_files = test_*.py check_*.py
python_classes = Test* Check*
python_functions = test_ check_

This tells pytest to also look for files named check_*.py and functions starting with check_.