Fixtures and Parametrize

pytest becomes even more powerful with fixtures and parameterized tests.

These tools help you reduce repeated code and test many inputs easily.

What Is a Fixture?

A fixture is reusable setup code for tests.

Use fixtures when many tests need the same data or objects.

Examples:

• sample user data
• database connection
• test file
• shared list

Why Fixtures Matter

Fixtures help you:

• remove repeated setup code
• keep tests cleaner
• reuse test data
• improve readability

Basic Fixture Example

import pytest

@pytest.fixture
def numbers():
    return [1, 2, 3]

Use the fixture:

def test_length(numbers):
    assert len(numbers) == 3

def test_first(numbers):
    assert numbers[0] == 1

Example Output

2 passed

How It Works

pytest sees the fixture name as a function parameter and provides the value automatically.

Another Fixture Example

import pytest

@pytest.fixture
def user():
    return {"name": "Maya", "active": True}

def test_name(user):
    assert user["name"] == "Maya"

What Is Parametrize?

Sometimes one test should run with many inputs.

Use:

@pytest.mark.parametrize

Basic Example

import pytest

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

@pytest.mark.parametrize(
    "a,b,expected",
    [
        (2, 3, 5),
        (1, 1, 2),
        (0, 5, 5),
    ]
)
def test_add(a, b, expected):
    assert add(a, b) == expected

Example Output

3 passed

Each row becomes a separate test case.

Why Parametrize Matters

It helps you:

• test many values quickly
• avoid repeated test functions
• keep tests short and clear

Combine Fixture + Parametrize

import pytest

@pytest.fixture
def base():
    return 10

@pytest.mark.parametrize("value", [1, 2, 3])
def test_total(base, value):
    assert base + value > 10

Code Along

Create a fixture named items that returns:

["Pen", "Book"]

Write two tests using it.

Mini Challenge

Create function:

def square(n):
    return n * n

Use parametrize to test:

• 2 → 4
• 3 → 9
• 5 → 25

Expected output:

3 passed

Real World Use Case

Teams use fixtures for test users, database setup, API clients, files, and reusable environments.

Quiz

1. What is a fixture?
2. Why use fixtures?
3. What does parametrize do?
4. Why is parametrize useful?

Assignment

Create a fixture with user data and two tests that use it.

Summary

You learned how fixtures reuse setup code and how parametrize runs one test with many inputs.