Testing python code with pytest lib

Prerequisites

Create virtual environment: python3 -m venv myenv Start virtual environment: . myenv/bin/activate Install dependencies: pip3 install -r requirements.txt

With pytest you can select which tests to run by decorators, run parallel tests, and continue running where you stopped etc. But pytest requires intallation of pytest. The python built in "unittest" does not have as much functionality as pytest but unittest does not require installation of any third part lib so for smaller projects unittest could be an alternative.

Naming tests

Files

It is good practise to always name your files, that contains your test cases, starting with "test_", like test_my_class.py. But the file names can also end with "_test.py". Running pytest without mentioning a filename will run all files of format test_*.py or *_test.py in the current directory and subdirectories but not a file named testMyclass.py or a_test_file.py.

Test cases

Pytest requires the test function names to start with test* so it will not run any function in the files that does not start with test*.

Running

All tests

You run your tests from the project root folder by for example executing: pytest or pytest <filename>
(-v stands for verbose and gives extra output)

Only tests matching specific name

To only execute the test functions containing a string in its name we can use the following syntax: pytest -k <substring>

Only tests with specific marker

To only execute the test functions that has a specific marker: pytest -m <markername>
For example, a test decorated with @pytest.mark.great can be executed with pytest -m great
(NOTE To get rid of marker warnings, declare custom markers in pytest.ini file)

Example

Lets say you have a structure like this:

project/
|
|-- src/
|   |-- my_program.py
|   |-- __init__.py
|
|-- tests/
|   |-- test_my_program.py
|   |-- prov_my_program.py
|   |-- my_program_test.py
|   |-- __init__.py
|
|-- test_my_project.py
|-- do_test_my_program.py

my_program.py contains your program code. All other files contains unit tests. In this case, if you run pytest in your project folder, all tests in test_my_project.py, tests/test_my_program.py and tests/my_program_test.py will be executed, but not do_test_my_program.py or tests/prov_my_program.py.

Source

https://www.tutorialspoint.com/pytest