Unit testing with pytest
Introduction to Testing in Python
Alexander Levin
Data Scientist
What is a unit test
Unit - the smallest working part that can be tested.
- Examples of units: functions, methods, classes, modules, etc.
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Unit testing - software testing method.
- Unit testing allows one to scrutinize the correctness of a unit.
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Test case - a set of unit inputs and expected outputs.
- Test case summarizes a particular piece of the problem.
Why to use unit tests
Unit tests - are a foundation for testing "the bigger picture" of the software.
Use cases:
- When bugs found
- During development
- After implemented changes
How to create a unit test
Step-by-step:
- Decide which units to test
- Define test cases (the creative part):
- "What are the possible unit outcomes?"
- "How can one use the unit?"
- "How should the unit behave in all those cases?"
- Write code for each test case
- Run the tests and analyze the results
Creating a unit test: example
Unit to test:
# Function for a sum of elements
def sum_of_arr(array:list) -> int:
return sum(array)
Test cases:
- Input is a list of numbers (as expected) - should return the
sum - Input is an empty list - should return
0 - Input is a list containing one
number- should return thenumber
Creating a unit test: code
# Test Case 1: regular array
def test_regular():
assert sum_of_arr([1, 2, 3]) == 6
assert sum_of_arr([100, 150]) == 250
# Test Case 2: empty list
def test_empty():
assert sum_of_arr([]) == 0
# Test Case 3: one number
def test_one_number():
assert sum_of_arr([10]) == 10
assert sum_of_arr([0]) == 0
Summary
Unit test - a test that verifies that a unit works as expected.
Test case - inputs and outputs summarizing a particular piece of the problem.
Use cases:
- When bugs found
- During development
- After implemented changes
Defining test cases - involves creativity.
Let's practice!
Introduction to Testing in Python
