Test modules in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest test discovery

Given the following test module, what will pytest report when run?

PyTest

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

def test_subtraction():
    assert 2 - 1 == 1

class TestMath:
    def test_multiply(self):
        assert 2 * 3 == 6

    def helper(self):
        return 5

A 3 passed tests

B 2 passed tests, 1 skipped

C 2 passed tests

D 1 passed test, 2 failed

💡 Hint

pytest discovers functions starting with 'test_' and methods inside classes named 'Test' starting with 'test_'.

pytest will find test_addition, test_subtraction, and test_multiply inside TestMath. The method helper is ignored because it does not start with 'test_'. All three tests pass.

❓ assertion

intermediate

Correct assertion for checking exception in pytest

Which assertion correctly tests that a function raises a ValueError when called with invalid input?

PyTest

def func(x):
    if x < 0:
        raise ValueError("Negative value")
    return x

A assert func(-1) raises ValueError

B assert func(-1) == ValueError

C

with pytest.raises(ValueError):
    func(-1)

D assertRaises(ValueError, func, -1)

💡 Hint

Use pytest's context manager to check exceptions.

Option C uses pytest.raises context manager correctly to check for exceptions. Option C compares return value to exception class, which is incorrect. Option C is invalid syntax. Option C is unittest style, not pytest.

🔧 Debug

advanced

Identify the cause of test not running

Why does pytest not run the test method in this module?

PyTest

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

A Class name does not start with 'Test', so pytest ignores it.

B The assert statement is incorrect and causes a syntax error.

C Method name does not start with 'test_', so pytest ignores it.

D The division operator is invalid in Python.

💡 Hint

pytest requires test classes to start with 'Test'.

pytest discovers test classes only if their names start with 'Test'. Here, the class is named 'math_tests' (lowercase 'm'), so pytest ignores it. The method name is correct, and the assert and division are valid.

❓ framework

advanced

Best practice for test module organization

Which option describes the best practice for organizing test modules in a pytest project?

A Write all tests in a single large file named 'all_tests.py'.

B Put all tests inside the main application modules to keep code together.

C Name test files with any name and place them randomly in the project.

D Place test files in a separate 'tests' directory with filenames starting with 'test_'.

💡 Hint

pytest automatically discovers tests in files named 'test_*.py' or '*_test.py'.

Option D follows pytest conventions: tests in a separate 'tests' folder and files named starting with 'test_'. This helps pytest find and run tests easily. Other options reduce clarity and maintainability.

🧠 Conceptual

expert

Understanding pytest fixture scope impact on test modules

Consider a pytest fixture defined with scope='module'. What is the impact of this scope on tests within the same module?

A The fixture is created once for the entire test session and shared globally.

B The fixture is created once per module and shared by all tests in that module.

C The fixture is created once per test class and shared only within that class.

D The fixture is created once per test function and destroyed after each test.

💡 Hint

Fixture scopes control how often the fixture setup runs.

Scope='module' means the fixture runs once when the module starts and is reused by all tests in that module. This improves performance when setup is expensive. Other scopes are 'function', 'class', and 'session'.

Practice

1. What is the correct way to name a Python file so that pytest recognizes it as a test module?

easy

A. The file name can be anything as long as it contains tests.

B. The file name should start with check_.

C. The file name should be pytest_module.py.

D. The file name should start with test_ or end with _test.py.

Solution

1. Step 1: Understand pytest file naming conventions

   pytest automatically discovers test files if their names start with test_ or end with _test.py.

2. Step 2: Evaluate each option

   Only The file name should start with test_ or end with _test.py. matches the correct naming pattern for pytest to find test modules automatically.

3. Final Answer:

   The file name should start with test_ or end with _test.py. -> Option D

4. Quick Check:

   pytest test file naming = start with test_ or end with _test.py [OK]

Hint: Remember test files start with test_ or end with _test.py [OK]

Common Mistakes:

• Assuming any file with tests is recognized
• Using incorrect prefixes like check_
• Naming files without .py extension

2. Which of the following is the correct syntax for a test function inside a pytest test module?

easy

A. def test_function():

B. def check_function():

C. def function_test():

D. def testing_function():

Solution

1. Step 1: Recall pytest test function naming rules

   pytest runs functions that start with test_ automatically as tests.

2. Step 2: Match options with naming rule

   Only def test_function(): defines a function starting with test_, so pytest will recognize it as a test.

3. Final Answer:

   def test_function(): -> Option A

4. Quick Check:

   Test functions start with test_ [OK]

Hint: Test functions must start with test_ to run automatically [OK]

Common Mistakes:

• Naming test functions without test_ prefix
• Using other prefixes like check_ or testing_
• Forgetting to define functions with def

3. Given the following test module test_sample.py with these functions:

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

def add():
    return 1 + 1

def test_subtract():
    assert 2 - 1 == 1

Which functions will pytest run as tests?

medium

A. All three functions

B. Only add

C. test_add and test_subtract

D. Only test_add

Solution

1. Step 1: Identify pytest test function naming

   pytest runs functions starting with test_ automatically as tests.

2. Step 2: Check each function name

   test_add and test_subtract start with test_, so pytest runs them. add does not start with test_, so it is ignored.

3. Final Answer:

   test_add and test_subtract -> Option C

4. Quick Check:

   Functions starting with test_ run as tests [OK]

Hint: Only functions starting with test_ run as tests [OK]

Common Mistakes:

• Thinking all functions in test file run as tests
• Confusing helper functions with test functions
• Ignoring function name prefixes

4. You have a test module named test_math.py with this code:

def test_multiply():
    assert 2 * 3 == 5

When you run pytest, what will happen?

medium

A. The test will fail because the assertion is incorrect.

B. pytest will not find any tests to run.

C. pytest will skip the test because of a syntax error.

D. The test will pass because 2 * 3 equals 6.

Solution

1. Step 1: Analyze the assertion in test_multiply

   The assertion checks if 2 * 3 == 5, which is false because 2 * 3 equals 6.

2. Step 2: Understand pytest test result

   pytest runs the test and finds the assertion false, so the test fails.

3. Final Answer:

   The test will fail because the assertion is incorrect. -> Option A

4. Quick Check:

   False assertion causes test failure [OK]

Hint: Check if assertion condition is true or false [OK]

Common Mistakes:

• Assuming test passes despite wrong assertion
• Confusing syntax errors with assertion failures
• Thinking pytest skips failing tests

5. You want to organize tests for a calculator app. You create two files: test_add.py and test_subtract.py. Each file has multiple test functions starting with test_. How does pytest handle these test modules when you run pytest in the folder?

hard

A. pytest requires you to specify each test module to run tests.

B. pytest runs all test functions from both modules automatically.

C. pytest runs only tests from the first module alphabetically.

D. pytest runs tests only if you import modules manually.

Solution

1. Step 1: Understand pytest test discovery

   pytest automatically finds all test modules named with test_ prefix and runs all test functions inside them.

2. Step 2: Apply to multiple test modules

   When running pytest in the folder, it collects tests from both test_add.py and test_subtract.py and runs all test functions starting with test_.

3. Final Answer:

   pytest runs all test functions from both modules automatically. -> Option B

4. Quick Check:

   pytest auto-discovers all test modules and functions [OK]

Hint: pytest runs all test_ modules and functions in folder automatically [OK]

Common Mistakes:

• Thinking pytest runs only one module at a time
• Believing manual imports are needed for tests
• Assuming tests must be specified explicitly