with pytest.raises(TypeError):

Testing Patterns

Meaning

The `with pytest.raises(TypeError):` context manager asserts that the code block inside raises a TypeError exception; if the block does not raise the expected exception, the test fails.

Primary Function

Testing

Communicative Purpose

Verify that a specific exception is raised by a piece of code during testing.

Pattern

with pytest.raises(;):

Core Structure

with pytest.raises(;):

Função primária

Testing

Propósito comunicativo

Verify that a specific exception is raised by a piece of code during testing.

Situações de gatilho

When writing unit tests to ensure a function raises a TypeError for invalid input; when checking that error handling code works; when validating API contracts.

Contextos

Python test suites using pytest; any project that uses pytest for testing.

Padrão

with pytest.raises(;):

Estrutura central

with pytest.raises(;):

Slots de substituição

exception_type: the exception class expected to be raised (e.g., TypeError, ValueError)

Colocados típicos

assert
pytest.mark
test functions
fixture setup

Substituições comuns

Using other exception types like ValueError
KeyError
using match parameter to check exception message: with pytest.raises(ValueError
match='invalid'):

Erros comuns

Forgetting to indent the block under the with statement; expecting the wrong exception type; using pytest.raises outside a test function; not asserting that the block actually runs (i.e., empty block).

Similar / contraste

pytest.raises vs. assertRaises in unittest; using try/except to catch exceptions manually; using pytest.warns for warnings.

Interferências

Coming from JUnit: may expect assertThrows syntax; from other languages: may think need to catch exception manually.

Família do chunk

pytest.raises
pytest.warns
assertRaises
try/except

Nuance

The context manager swallows the exception; code after the with block only runs if no exception or if exception matches; if you need to inspect the exception value, use `with pytest.raises(TypeError) as exc_info:` to access exc_info.value.

Efeito pragmático

Makes test intent explicit and ensures proper exception handling verification.

Dica de memória

Think 'with pytest.raises' as 'expect this error'.

Nota

Remember to indent the block under the with statement; the exception is swallowed unless captured via 'as exc_info' to inspect its value.

Upgrade path

with pytest.raises(TypeError) as exc_info: ... to inspect exception attributes

Frequência: HighFormulaicidade: Semi-fixedTipo de construção: context_managerPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Medium-term

Examples

import pytest\n\ndef add(a, b):\n if not isinstance(a, (int, float)) or not isinstance(b, (int, float)):\n raise TypeError("Arguments must be numbers")\n return a + b\n\ndef test_add_type_error():\n with pytest.raises(TypeError):\n add("2", 3)

import pytest\n\nclass ValidationError(Exception):\n pass\n\ndef validate_age(age):\n if age < 0:\n raise ValidationError("Age cannot be negative")\n return age\n\ndef test_validate_negative():\n with pytest.raises(ValidationError):\n validate_age(-5)

import pytest\n\ndef divide(a, b):\n if b == 0:\n raise ZeroDivisionError("division by zero")\n return a / b\n\ndef test_divide_by_zero_message():\n with pytest.raises(ZeroDivisionError, match="division by zero"):\n divide(5, 0)