How to Efficiently Run Unit Tests from a Separate Test Directory in Python?

How to Run Unit Tests in a Common Test Directory Structure

In Python, it's common practice to organize unit tests in a separate test directory. However, this raises the question of how to execute these tests efficiently.

Problem

When attempting to run python test_antigravity.py from within the test directory, the import of the antigravity module fails due to the module not being on the path. Modifying the PYTHONPATH or using other search path tricks may be feasible, but they lack simplicity, especially for users who simply want to verify the test results.

Solution

The recommended approach is to utilize the unittest command line interface. Its TestLoader class adds the necessary directory to sys.path, resolving the path issue.

For example, in a directory structure like this:

new_project
├── antigravity.py
└── test_antigravity.py

You can execute the tests with:

$ cd new_project
$ python -m unittest test_antigravity

For a directory structure like the one provided:

new_project
├── antigravity
│   ├── __init__.py
│   └── antigravity.py
└── test
    ├── __init__.py
    └── test_antigravity.py

You can achieve similar functionality by declaring both antigravity and test as packages with __init__.py files. In the test modules, you can import the antigravity package and its modules as usual.

Running Specific Tests

To run a single test module, such as test_antigravity.py:

$ cd new_project
$ python -m unittest test.test_antigravity

You can also run individual test cases or methods:

$ python -m unittest test.test_antigravity.GravityTestCase
$ python -m unittest test.test_antigravity.GravityTestCase.test_method

Running All Tests

You can use test discovery to automatically run all tests. This requires that the test modules and packages are named test*.py (customizable via the -p or --pattern flag):

$ cd new_project
$ python -m unittest discover

For users who prefer simplicity, you can instruct them to run the following command:

To run the unit tests, do:
$ python -m unittest discover

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