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Running Tests with pytest

Welcome to the modernized test system! We now use pytest instead of the old custom testing framework.

Quick Start

From the course folder, run:

# Run all tests
pytest

# Run tests for a specific set
pytest set1/
pytest set2/

# Run a specific test file
pytest set1/test_set1_exercise1.py

# Run tests with more detail
pytest -v

# Run tests and stop at first failure
pytest -x

What You'll See

When you run tests, you'll see beautiful output with progress bars and colors thanks to pytest-sugar:

 set1/test_set1_exercise1.py ✓✓✓✓✓                                     5% ██
 set1/test_set1_git_setup.py ✗✗✗✗✗                                    10% ███

When a test fails, you'll see exactly what went wrong with helpful messages and clear diffs showing what you returned vs what was expected.

Understanding Test Markers

Tests are marked with special tags that tell you what they're testing:

  • @pytest.mark.set1 through @pytest.mark.set8 - Which exercise set
  • @pytest.mark.mock_input - Tests that simulate user input
  • @pytest.mark.timeout - Tests that will stop if they run too long (usually 3-10 seconds)
  • @pytest.mark.api_call - Tests that make real API calls (might be slower)
  • @pytest.mark.slow - Optional tests that take longer (like visualizations)

Running Specific Types of Tests

# Run only Set 3 tests
pytest -m set3

# Skip slow tests
pytest -m "not slow"

# Run only tests with API calls
pytest -m api_call

# Run tests that use mock input
pytest -m mock_input

When Tests Time Out

If your code has an infinite loop, pytest will automatically stop it after a few seconds and show you which test timed out. This prevents your terminal from hanging forever!

Reading Test Failures

Pytest shows you three things when a test fails:

  1. What the test was checking - The test name and description
  2. What you returned - Your function's actual output
  3. What was expected - The correct answer

For example:

AssertionError: 
add_5(10)
Expected: 15
Got:      10

💡 Remember: add_5 should ADD 5 to the number, not return it unchanged!

Tips

  • Read the error messages carefully - They're designed to help you understand what went wrong
  • Run one test file at a time while working on an exercise: pytest set2/test_set2_exercise0.py
  • Use -v (verbose) if you want to see every single test name as it runs
  • Use -x to stop at the first failure so you can focus on one problem at a time
  • Use --lf to re-run only the tests that failed last time

Common Commands

# Most useful during development:
pytest set2/ -v -x          # Run Set 2, verbose, stop at first failure

# When you want to see everything:
pytest -v                   # Run all tests with details

# When you're fixing failures:
pytest --lf                 # Run only last failed tests

# To see what tests exist:
pytest --collect-only       # Show all tests without running them

# Check if your code even loads:
python -m py_compile set2/exercise0.py

Need Help?

  • Read the test names - they describe what they're testing
  • Look at the error messages - they explain what went wrong
  • Check the test file itself - it shows what the test expects
  • Ask in the course forum if you're stuck!

What Changed from the Old System?

Before: python tests.py with custom test framework
Now: pytest with industry-standard testing framework

Why?

  • pytest is what professional developers use in the real world
  • Better error messages and diffs
  • Faster execution
  • More helpful output
  • Skills you'll use in your career

The tests themselves check the same things - we just modernized how they run!