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Testing & modern typing

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

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Mock datetime with time-machine in Python

Use the time-machine library to travel to a fixed datetime when running tests or scripts, mocking datetime.utcnow().

from time_machine import travel
from datetime import datetime


@travel("2020-01-01 10:30:00")
def check_date():
    return datetime.utcnow()


if __name__ == "__main__":
    print(check_date())

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Testing & modern typing easy

Mock datetime.now to freeze time in Python

Use unittest.mock.patch to replace datetime.now with a fixed value so your code always sees the same time during tests.

datetime mock unittest

Python

from datetime import datetime
from unittest.mock import patch

def current_message():
    now = datetime.now()
    return f"Current time: {now:%Y-%m-%d %H:%M:%S}"

if __name__ == "__main__":
    with patch("__main__.datetime") as mock_dt:
        mock_dt.now.return_value = datetime(2024, 3, 15, 10, 30, 0)
        prin…

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Testing & modern typing easy

NamedTuple typed record in Python

Define a lightweight immutable record with type hints using typing.NamedTuple; access fields by name and unpack like a tuple.

namedtuple typing records

Python

from typing import NamedTuple


class Point(NamedTuple):
    x: float
    y: float
    label: str = "origin"


if __name__ == "__main__":
    p = Point(3.5, -2.0, "A")
    print(p)
    print(f"x={p.x}, y={p.y}, label={p.label}")
    print("is tuple:", isinstance(p, tuple))

    q = Point(1.0, 1.0)
    print(q)

    # …

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Testing & modern typing easy

Table-Driven Tests in Python (unittest)

Run a single unittest test against many input cases using a list of tuples and subTest.

unittest table-driven testing

Python

import unittest

def add(a, b):
    return a + b

class TestAddFunction(unittest.TestCase):

    def test_add_with_table(self):
        cases = [
            (1, 2, 3),
            (-1, 1, 0),
            (0, 0, 0),
            (2, -3, -1),
        ]
        for x, y, expected in cases:
            with self.subTest(x…

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