Python Coverage refers to measuring which parts of your Python code are being executed during testing. It is a critical tool for ensuring comprehensive test coverage, helping developers understand which lines of code are tested and which are not. Here’s a deeper dive into how to use Python Coverage effectively:
Getting Started with Python Coverage
Installation
You can install the coverage module using pip:
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pip install coverage
Running Tests with Coverage
To measure code coverage, you run your tests through the coverage tool. Here’s a basic example:
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coverage run -m unittest discover
This command runs all tests discovered by unittest while tracking code coverage.
Generating Coverage Report
After running tests, you can generate a coverage report. Coverage provides different report formats, including terminal output, HTML, and XML. Here’s how to generate a simple text report:
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coverage report
For a more detailed HTML report, use:
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coverage html
This will create an htmlcov directory with the coverage report. You can open index.html in a browser to view the report.
Configuring Coverage
You can configure coverage settings in a .coveragerc file. Here’s an example configuration:
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[run]
branch = True
source = my_package
[report]
show_missing = True
• branch: Ensures branch coverage is measured.
• source: Specifies the source code directories.
• show_missing: Displays lines that were not executed.
Advanced Usage
• Excluding Files: To exclude files or directories from coverage, use the omit option in the .coveragerc file:
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[run]
omit =
/tests/
/migrations/
• Combining Coverage Data: To merge coverage data from multiple runs, use:
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coverage combine
• Checking Coverage Thresholds: Set minimum coverage thresholds to enforce code quality:
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coverage report –fail-under=80
This command will fail the build if the coverage is below 80%.
Example Usage
Here’s a complete example of running tests with coverage and generating a report:
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# Install coverage
pip install coverage
Run tests with coverage
coverage run -m unittest discover
Generate a terminal report
coverage report
Generate an HTML report
coverage html
Conclusion
Python Coverage is a powerful tool for ensuring your tests cover all parts of your codebase. By integrating it into your development workflow, you can improve code quality, catch bugs early, and maintain high test coverage standards. Happy coding!
