How to Use pytest Naming Convention for Test Discovery

In pytest, test files should start with test_ or end with _test.py, and test functions or methods must start with test_. This naming convention allows pytest to automatically find and run your tests without extra configuration.

Syntax

pytest uses specific naming rules to find tests automatically:

• Test files: Must be named starting with test_ or ending with _test.py.
• Test functions or methods: Must start with test_.
• Test classes: Should start with Test and not have an __init__ method.

Following these rules ensures pytest discovers your tests without extra setup.

python

test_example.py

def test_addition():
    assert 1 + 1 == 2

class TestMath:
    def test_subtraction(self):
        assert 2 - 1 == 1

Example

This example shows a test file named test_math.py with two test functions and one test class. All follow pytest naming conventions, so pytest will find and run them automatically.

python

test_math.py

def test_multiply():
    assert 3 * 4 == 12

class TestDivision:
    def test_divide(self):
        assert 10 / 2 == 5

    def test_divide_by_zero(self):
        import pytest
        with pytest.raises(ZeroDivisionError):
            _ = 1 / 0

Output

============================= test session starts ==============================
collected 3 items

test_math.py ...                                                        [100%]

============================== 3 passed in 0.01s ===============================

Common Pitfalls

Common mistakes include:

• Naming test files or functions without the test_ prefix, so pytest skips them.
• Using Test classes with an __init__ method, which pytest does not support.
• Defining test functions inside classes that do not start with Test.

Always follow the naming rules strictly to avoid missing tests.

python

wrong_name.py

def add_test():
    assert 1 + 1 == 2

class MathTests:
    def test_subtract(self):
        assert 2 - 1 == 1

# Correct naming

test_correct.py

def test_add():
    assert 1 + 1 == 2

class TestMath:
    def test_subtract(self):
        assert 2 - 1 == 1

Quick Reference

Item	Naming Rule
Test file	Starts with 'test_' or ends with '_test.py'
Test function or method	Starts with 'test_'
Test class	Starts with 'Test' and no __init__ method
Non-test code	Should not start with 'test_' to avoid confusion

Key Takeaways

Always name test files starting with 'test_' or ending with '_test.py' for pytest to find them.

Prefix test functions and methods with 'test_' to ensure pytest discovers and runs them.

Test classes should start with 'Test' and must not have an __init__ method.

Incorrect naming causes pytest to skip tests silently, so follow conventions strictly.

Use the quick reference table to remember pytest naming rules easily.