✅ Unit Testing

Unit tests check small pieces of code in isolation. They should run fast and avoid external dependencies (network, filesystem, real time).

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✅ Two Common Tools

1) unittest (built-in)

• Comes with Python.
• Uses test classes and methods.
• Great when you can't install extra dependencies.

2) pytest (third-party)

• Very popular in the Python ecosystem.
• Uses simple assert statements.
• Excellent output and fixtures.

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✅ Arrange / Act / Assert (AAA)

Most unit tests follow a simple pattern:

1) Arrange: set up inputs 2) Act: call the function 3) Assert: check the result

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✅ What to Unit Test

• Business rules and pure logic
• Edge cases (empty input, boundaries)
• Error paths (invalid input)

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🔍 Key Takeaways

• Unit tests are the fastest and cheapest tests.
• Keep unit tests independent and deterministic.
• Prefer small functions with clear inputs/outputs.

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Next: Test-Driven Development →