pytest-cov for coverage - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is pytest-cov used for?

pytest-cov is a plugin for pytest that measures how much of your code is tested by your tests. It shows which parts of the code were run and which were missed.

beginner

How do you install pytest-cov?

You install it using pip with the command: pip install pytest-cov. This adds coverage support to your pytest tests.

beginner

What command runs tests with coverage report in the terminal?

Use pytest --cov=your_package to run tests and see coverage in the terminal. Replace your_package with your code folder or module name.

intermediate

How can you generate an HTML coverage report with pytest-cov?

Add --cov-report=html to your pytest command. For example: pytest --cov=your_package --cov-report=html. This creates a folder htmlcov with a detailed report you can open in a browser.

beginner

Why is measuring test coverage important?

Coverage helps you see which parts of your code are tested and which are not. This helps find missing tests and improve code quality by making sure important parts are checked.

What does pytest-cov measure?

A Number of tests passed

B How fast your tests run

C How much of your code is executed by tests

D Memory usage during tests

pytest-cov measures code coverage, which is how much of your code is run when tests execute.

Which command installs pytest-cov?

A pip install pytest-cov

B npm install pytest-cov

C pytest install cov

D pip install coverage

The correct command is pip install pytest-cov to add the coverage plugin for pytest.

How do you run tests with coverage for a package named app?

A pytest --run app

B pytest --coverage app

C pytest --cov-report=app

D pytest --cov=app

Use pytest --cov=app to run tests and measure coverage for the app package.

What does --cov-report=html do?

A Generates an HTML coverage report

B Runs tests in HTML mode

C Saves coverage data as HTML files

D Disables coverage reporting

This option creates a detailed HTML report showing coverage results in a browser-friendly format.

Why should you check test coverage?

A To speed up tests

B To find untested code parts

C To reduce code size

D To increase test failures

Checking coverage helps identify code that has no tests, so you can add tests and improve quality.

Explain how to use pytest-cov to measure and report test coverage for a Python project.

Think about installation, running tests, and generating reports.

Why is test coverage useful and how can pytest-cov help improve your tests?

Consider the benefits of knowing what your tests cover.

Practice

1. What is the main purpose of using pytest-cov in your testing workflow?

easy

A. To generate test data automatically

B. To speed up test execution time

C. To automatically fix failing tests

D. To measure how much of your code is covered by tests

Solution

1. Step 1: Understand pytest-cov functionality

   pytest-cov is a plugin that measures code coverage during test runs.

2. Step 2: Identify the main goal of coverage tools

   Coverage tools show which parts of code are tested and which are not.

3. Final Answer:

   To measure how much of your code is covered by tests -> Option D

4. Quick Check:

   pytest-cov = code coverage measurement [OK]

Hint: Coverage means how much code tests run over [OK]

Common Mistakes:

• Confusing coverage with test speed
• Thinking pytest-cov fixes tests automatically
• Assuming pytest-cov generates test data

2. Which command correctly runs pytest with coverage for a package named myapp?

easy

A. pytest -cov myapp

B. pytest --cov=myapp

C. pytest --coverage myapp

D. pytest --cov tests/

Solution

1. Step 1: Recall correct pytest-cov syntax

   The correct option to enable coverage is --cov=package_name.

2. Step 2: Compare options

   pytest --cov=myapp uses --cov=myapp, which is the correct syntax. pytest --cov tests/ would incorrectly target the tests directory instead of the myapp package.

3. Final Answer:

   pytest --cov=myapp -> Option B

4. Quick Check:

   Use --cov=package [OK]

Hint: Use equal sign with --cov like --cov=package [OK]

Common Mistakes:

• Targeting tests directory instead of the package
• Using -cov instead of --cov
• Using --coverage instead of --cov

3. Given this command run:
pytest --cov=myapp tests/test_module.py
What output will you expect related to coverage?

medium

A. A report showing coverage percentage for myapp package

B. A list of all tests run without coverage info

C. An error saying coverage option is invalid

D. Coverage report for tests directory only

Solution

1. Step 1: Understand coverage target

   The --cov=myapp option measures coverage for the myapp package, not tests.

2. Step 2: Predict output

   Running tests in tests/test_module.py with coverage enabled will show coverage report for myapp code exercised by those tests.

3. Final Answer:

   A report showing coverage percentage for myapp package -> Option A

4. Quick Check:

   --cov=package shows coverage for that package [OK]

Hint: Coverage reports show tested code, not test files [OK]

Common Mistakes:

• Expecting coverage for test files instead of source code
• Thinking coverage option causes errors
• Confusing coverage report with test list output

4. You ran pytest --cov=myapp but no coverage report appeared. What is the most likely cause?

medium

A. You forgot to install pytest-cov plugin

B. You ran pytest without any test files

C. Your code has no functions to cover

D. You used wrong package name in --cov option

Solution

1. Step 1: Check plugin installation

   pytest-cov must be installed to enable coverage reporting.

2. Step 2: Understand symptoms

   If no coverage report appears, the plugin is likely missing or not activated.

3. Final Answer:

   You forgot to install pytest-cov plugin -> Option A

4. Quick Check:

   pytest-cov missing = no coverage report [OK]

Hint: Install pytest-cov to get coverage reports [OK]

Common Mistakes:

• Assuming coverage works without plugin installed
• Thinking coverage depends on code content
• Ignoring plugin installation errors

5. You want to generate an HTML coverage report for your package app using pytest-cov. Which command should you run?

hard

A. pytest --coverage=app --report=html

B. pytest --cov=app --html=coverage

C. pytest --cov=app --cov-report=html

D. pytest --cov app --html-report

Solution

1. Step 1: Recall pytest-cov report syntax

   The option --cov-report=html generates an HTML coverage report.

2. Step 2: Match correct command format

   pytest --cov=app --cov-report=html correctly uses --cov=app and --cov-report=html together.

3. Final Answer:

   pytest --cov=app --cov-report=html -> Option C

4. Quick Check:

   Use --cov-report=html for HTML coverage [OK]

Hint: Use --cov-report=html to get HTML coverage output [OK]

Common Mistakes:

• Using --html instead of --cov-report=html
• Omitting equal signs in options
• Confusing coverage options with test report options