Assert that a specific exception is raised during test execution.

Communicates the expectation that a particular exception will be raised, making the test's intent explicit.

When writing a test that expects a function or method to raise a specific exception under certain conditions.

Inside pytest test functions when validating error handling, edge cases, or failure modes of code under test.

with pytest.raises(ExceptionType):

with pytest.raises(ExceptionType):

ExceptionType: type of exception to catch (must be a subclass of BaseException)

• pytest
• test
• assert
• raise
• ValueError
• TypeError
• Exception
• match

• ValueError → TypeError
• KeyError
• AssertionError
• CustomException
• using pytest.raises(Exception) to catch any exception

1. Forgetting the colon after the exception type → SyntaxError: invalid syntax. 2. Using unittest's assertRaises incorrectly → test may pass incorrectly because exception not caught. 3. Forgetting to indent code under the with block → IndentationError or code runs outside context, causing false pass. 4. Catching too broad an exception (Exception) when a specific one is expected → test may pass for wrong exception, hiding bugs. 5. Using pytest.raises outside a test function → pytest raises MisplacedFixtureError.

pytest.raises vs unittest.TestCase.assertRaises: pytest.raises works as a context manager or callable, more flexible; unittest.assertRaises requires method call. pytest.raises vs pytest.warns: former asserts exception, latter asserts warning. pytest.raises vs pytest.raises(None): former asserts an exception is raised, latter asserts no exception is raised.

Coming from unittest: may forget to use the context manager form and write self.assertRaises(ValueError, func, *args) incorrectly, leading to missed assertions → use pytest.raises context manager or callable form. Coming from other languages: may expect try/except to swallow the exception → remember pytest.raises expects the exception to propagate to fail the test if not raised.

• pytest assertions
• testing idioms
• exception handling patterns

1. NOT to use when you need to assert that no exception is raised; use pytest.raises(None) or let code run and assert no exception. 2. Performance impact is negligible; only minimal context manager overhead. 3. Boundary: must be used inside a test function; using outside pytest raises MisplacedFixtureError; also the exception must be raised directly in the block unless using the callable form.

Ensures tests reliably verify error conditions, preventing false passes and increasing confidence in error handling code.

Like a safety net that catches the expected exception and fails the test if the net stays empty.

Used in pytest to assert that a specific exception is raised.

Using pytest.raises with the match parameter to assert exception message matches a regex, or using the callable form pytest.raises(Exception, func, *args) for more flexible testing.