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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

3 matches

Fuzz Test Random Bytes Input Crash in Python

A simple fuzz test generates random byte inputs and runs a parser to find unexpected crashes.

import random


def parse_header(data: bytes) -> dict:
    """Parse a fake binary header format."""
    if len(data) < 8:
        raise ValueError("header too short")

    magic = data[:4]
    if magic != b'PARS':
        raise ValueError("bad magic")

    version = data[4]
    if version != 1:
        raise ValueErro…

14 0 Open

Testing & modern typing easy

How to Assert Exceptions in Python with pytest.raises

Use pytest.raises as a context manager to assert that a function raises an expected exception and inspect its message in pytest tests.

pytest testing exceptions

Python

import pytest

def divide(a, b):
    if b == 0:
        raise ValueError("Cannot divide by zero")
    return a / b

def test_divide_by_zero():
    with pytest.raises(ValueError) as exc_info:
        divide(10, 0)
    assert str(exc_info.value) == "Cannot divide by zero"
    assert "zero" in str(exc_info.value)

def te…

14 0 Open

Testing & modern typing easy

How to use unittest mock side_effect with a sequence in Python

Demonstrates using Mock.side_effect with a list to return different values per call and raise an exception at a specific call in unittest.

unittest mock side_effect

Python

import unittest
from unittest.mock import Mock

class TestMockSideEffectSequence(unittest.TestCase):
    def test_side_effect_sequence(self):
        mock = Mock()
        mock.side_effect = [1, 2, 3, Exception("boom")]
        
        self.assertEqual(mock(), 1)
        self.assertEqual(mock(), 2)
        self.asser…

13 0 Open

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