Specifying Which Pytest Tests to Run from a File

In software development, testing is a crucial phase that ensures the application meets its requirements without defects. One of the popular testing frameworks in Python is `pytest`. It allows you to write simple unit tests as well as complex functional test cases. While setting up your testing environment with `pytest`, there may be situations where you want to run specific tests rather than your entire test suite. This article provides a comprehensive guide on how to specify which `pytest` tests to run from a file.

Overview of Pytest

`pytest` is a powerful testing framework that supports features such as:

• Auto-discovery of test modules and functions.
• Support for fixtures that manage setup and teardown of resources.
• Rich assertions and reporting.
• Extensibility through plugins.

You can run `pytest` using the command line interface (CLI), giving you flexibility in choosing subsets of tests.

Specifying Tests to Run

Running specific tests using `pytest` can be achieved via several techniques, and one of the most efficient ways is by specifying tests in a file. This approach is particularly useful for:

• Rerunning failed tests.
• Running a predefined list of critical tests for nightly runs.
• Custom test selections determined at runtime.

Running Tests Listed in a File

To run tests specified in a file, you can use the `--file` plugin provided by `pytest`. This allows you to list the tests you wish to run in a plain text file, and `pytest` will execute only those tests. Below are the steps to utilize this feature:

1. Create a Test List File: Create a text file listing the test paths you wish to run. Each line should specify one test in the format ```<path-to-file>``::``<test-function>```.
   Example of `test_selection.txt`:

• Parametrization: You can parameterize your tests for different input values and scenarios. You might have separate test files where each line corresponds to a different parameter set.
• Custom Tags (Markers): Use markers to tag tests with metadata and include them in your test file by marker type.