Unit-level regression tests
Validate a small function or class behavior with explicit expected values.
Python · Module
unittest
Python’s unittest module provides a standard framework for automating unit tests, sharing setup and cleanup, grouping tests, and reporting results. Tests are commonly organized as TestCase instances and run through the module’s command-line interface.
How it works
The module models tests as TestCase instances, usually created by subclassing TestCase and adding methods whose names begin with test. Assertions check expected behavior, while the command-line runner can execute modules, classes, methods, or discovered tests and report results.
Syntax
python -m unittest [options] [module[.Class[.method]] ...]Parameters
| Name | Type | Description |
|---|---|---|
target | module, class, or method name | A module, TestCase class, or individual test method target passed to the command-line runner. |
Returns
A test run report; failures and errors are reported by the runner.
Key points
- The framework supports automated execution and reusable setup or cleanup around tests.
- Tests can be grouped into collections while remaining independent from how results are reported.
- A test case represents one scenario whose behavior is arranged and checked.
- TestCase instances are the concrete objects used to represent individual tests.
- Use -v with the command-line runner when diagnostic output needs to be more detailed.
Common mistakes
- A test must be represented by a TestCase instance, typically produced from a TestCase subclass.
- Use the module runner rather than relying only on direct function calls when executing test suites.
Example: A minimal unittest test
import unittest
def add(left, right):
return left + right
class AddTests(unittest.TestCase):
def test_adds_numbers(self):
self.assertEqual(add(2, 3), 5)
if __name__ == "__main__":
unittest.main()Defines a TestCase subclass, checks an expected result, and runs the test module directly.
When to use it
Targeted command-line execution
Run a complete test module or selected dotted test target from a shell.
Suite organization
Organize multiple test cases into reusable collections for a larger suite.
Interview questions
QHow are tests represented?
A TestCase is the basic unit of a unittest test. Create one by subclassing unittest.TestCase and define test methods containing assertions.
Follow-up: How can one test be run without running its whole module? Pass the dotted module, class, and method name to python -m unittest.
QHow do you run selected tests?
The command supports module names, TestCase class names, and individual test method names. Add -v to request more detailed output.
Follow-up: What is the command-line shortcut for discovery? Running python -m unittest without a target is equivalent to unittest discover.
QWhat capabilities does unittest provide beyond assertions?
unittest supports test automation, shared setup and shutdown code, grouping tests into collections, and separating tests from the reporting framework.
Follow-up: Which mechanism finds tests automatically? Test discovery can locate tests across a project, while explicit targets restrict execution to chosen tests.
Related
unittest.TestCaseunittest.TestSuiteunittest.TestLoaderunittest.mainunittest discover