Test discovery and naming conventions
Overview
Before testing code, we need a way to find and run those tests. **Test discovery is how tools like pytest find your test files and functions automatically.** To see this, imagine we have a function that checks if a student passed their exams. Here is a working test file: ```python # File: test_marks.py def has_passed(marks): return marks > 40 def test_has_passed(): assert has_passed(50) == True ``` When we run the command `pytest`, it looks for files starting with `test_` or ending with `_test.py`. Inside those files, it looks for functions starting with `test_`. Because our file is named `test_marks.py` and our function is named `test_has_passed`, pytest finds and runs it. Now, let us look at a similar test, but one step is blank: ```python # File: test_attendance.py def is_present(days): return days > 75 def _______is_present(): assert is_present(80) == True ``` To make pytest find this test automatically, we must name the function `test_is_present`.
Without a naming rule, you would have to manually list every test file you want to run. Discovery rules save time and keep projects organized.
Where used: Pytest setups, CI/CD pipelines
Why learn this
- Running all tests in a project with one simple command.
Code walkthrough
# File: test_logic.py
def is_even(n):
return n % 2 == 0
def test_is_even():
result = is_even(4)
print('Test running')
assert result == True
test_is_even()Focus: def test_is_even():
Aha moment
# File: my_tests.py
def test_logic():
print('Checking logic')
assert True
print('Done')Prediction: If you run `pytest` in the folder containing this file, will it run `test_logic`?
Common guess: Yes, because the function starts with test_.
The file name `my_tests.py` does not start with `test_` or end with `_test.py`. pytest will not look inside it, so the test is skipped.
Common mistakes
- Forgetting the test_ prefix: If you name your function `check_passed` instead of `test_check_passed`, pytest will ignore it. Always start test function names with `test_`.
Recall questions
- Explain test discovery and naming conventions in your own words, as if to a classmate.
- What prefix must a test file have for pytest to find it automatically?
Understanding checks
What happens when you run pytest on this file?
pytest runs zero tests because verify_add does not start with test_.
Test discovery relies strictly on the `test_` prefix. Since `verify_add` does not start with `test_`, pytest ignores it entirely.
Will pytest find and run this test?
Yes, because the file ends with _test.py and the function starts with test_.
Files ending in `_test.py` are also valid for test discovery, and the function correctly starts with `test_`.
Practice tasks
Fix the naming
Given this code, change the names so that pytest will find and run the test.
Challenge
Name a test file and function
Write a test file named correctly for pytest. Inside it, write a test function named correctly that asserts `True`.
Continue learning
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