Test discovery rules in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Pytest test discovery with file naming

Given the following files in a directory, which files will pytest discover as test files by default?

PyTest

test_example.py
example_test.py
testexample.py
example.py

A All four files

B test_example.py only

C test_example.py, example_test.py, and testexample.py

D test_example.py and example_test.py only

💡 Hint

Pytest looks for files starting with 'test_' or ending with '_test.py'.

Pytest discovers test files that match the pattern test_*.py or *_test.py. So test_example.py and example_test.py are discovered. testexample.py and example.py do not match these patterns.

❓ assertion

intermediate

Pytest test function discovery rules

Which of the following function names will pytest discover as test functions inside a test file?

PyTest

def test_add(): pass
def add_test(): pass
def Test_add(): pass
def testAdd(): pass

A test_add and add_test

B Only test_add

C test_add, add_test, and Test_add

D All four functions

💡 Hint

Pytest looks for functions matching the 'test_*' pattern (starts with 'test_').

Pytest discovers test functions whose names match the default test_* pattern (using fnmatch), meaning they must start with test_ (lowercase 'test' followed by an underscore). Only test_add matches. add_test does not start with test_, Test_add starts with uppercase 'T', and testAdd lacks the underscore after 'test'.

🔧 Debug

advanced

Why is this test function not discovered by pytest?

Consider this test file named test_math.py: ```python def _test_subtract(): assert 5 - 3 == 2 ``` Why does pytest not run this test function?

PyTest

def _test_subtract():
    assert 5 - 3 == 2

A Function name starts with an underscore, so pytest ignores it

B Function name must be exactly 'test_subtract' to be discovered

C Function is missing a return statement

D Function is missing the @pytest.mark.test decorator

💡 Hint

Pytest ignores functions starting with underscore by default.

Pytest discovers functions starting with 'test' but not those starting with an underscore. The underscore prefix makes pytest ignore the function.

🧠 Conceptual

advanced

Pytest test class discovery rules

Which of the following classes will pytest discover test methods from inside a test file?

PyTest

class TestCalculator:
    def test_add(self): pass

class CalculatorTest:
    def test_subtract(self): pass

class testCalculator:
    def test_multiply(self): pass

class Test_calculator:
    def test_divide(self): pass

A TestCalculator and Test_calculator only

B All four classes

C TestCalculator, CalculatorTest, and Test_calculator

D TestCalculator only

💡 Hint

Pytest discovers classes starting with 'Test' (uppercase T) and ignores others.

Pytest discovers classes whose names start with 'Test' exactly (uppercase T). So TestCalculator and Test_calculator are discovered. CalculatorTest ends with 'Test' but does not start with it, so it is ignored. testCalculator starts with lowercase 't' so it is ignored.

❓ framework

expert

Customizing pytest test discovery patterns

You want pytest to discover test files that start with 'check_' instead of 'test_'. Which pytest configuration option should you set in pytest.ini to achieve this?

A

[pytest]
file_patterns = check_*.py

B

[pytest]
python_functions = check_*

C

[pytest]
python_files = check_*.py

D

[pytest]
test_file_pattern = check_*.py

💡 Hint

The option to change test file discovery pattern is 'python_files'.

In pytest.ini, the option python_files controls which file patterns pytest uses to discover test files. Setting python_files = check_*.py makes pytest look for files starting with 'check_'.