Test modules in PyTest - Build an Automation Script

Verify pytest test module execution and results

Preconditions (2)

Step 1: Open terminal or command prompt

Step 2: Navigate to the directory containing test_sample.py

Step 3: Run the command 'pytest test_sample.py'

Step 4: Observe the test execution output

Step 5: Verify that all test functions in the module run and their results are displayed

✅ Expected Result: pytest runs all tests in test_sample.py and shows a summary with pass/fail status for each test

Automation Requirements - pytest

Assertions Needed:

Verify that test functions execute without errors

Verify that pytest output includes test names and pass/fail status

Best Practices:

Use descriptive test function names starting with 'test_'

Keep tests independent and isolated

Use assert statements for validation

Organize tests in modules named test_*.py

Automated Solution

PyTest

import subprocess
import sys
import re

def test_pytest_module_execution():
    # Run pytest on the test_sample.py module
    result = subprocess.run([sys.executable, '-m', 'pytest', 'test_sample.py', '--tb=short', '-q'], capture_output=True, text=True)
    output = result.stdout
    # Check pytest exited with code 0 (success)
    assert result.returncode == 0, f"pytest exited with code {result.returncode}"
    # Check output contains test function names and pass status
    assert re.search(r'test_function_one', output), "test_function_one not found in output"
    assert re.search(r'test_function_two', output), "test_function_two not found in output"
    assert re.search(r'\d+ passed', output), "No tests passed message found"

This test script runs pytest on the module test_sample.py using Python's subprocess module. It captures the output and return code.

We assert that pytest exits with code 0, meaning all tests passed. Then we check the output text to confirm the test function names appear and that the summary shows tests passed.

This approach verifies that the test module runs correctly and pytest reports results as expected.

Common Mistakes - 3 Pitfalls

Not capturing pytest output for verification

Using print statements instead of assert for validation

Running pytest without specifying the test module

Bonus Challenge

Now add data-driven testing with 3 different inputs for one test function in the module

Show Hint

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