What are Parametrized Tests and why use them?

Question

Accepted Answer

**Parametrized tests** run the **same test** with **different inputs**.

```python
import pytest

def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

# Basic parametrize
@pytest.mark.parametrize("input,expected", [
    (2, True),
    (3, True),
    (4, False),
    (17, True),
    (20, False),
    (-1, False),
    (0, False),
    (1, False),
])
def test_is_prime(input, expected):
    assert is_prime(input) == expected

# Multiple parameters
@pytest.mark.parametrize("a,b,expected", [
    (1, 2, 3),
    (-1, 1, 0),
    (0, 0, 0),
    (100, 200, 300),
])
def test_add(a, b, expected):
    assert a + b == expected

# IDs for better output
@pytest.mark.parametrize("input", [
    pytest.param(2, id="prime-2"),
    pytest.param(4, id="not-prime-4"),
    pytest.param(17, id="prime-17"),
])
def test_is_prime_with_ids(input):
    assert is_prime(input) == (input in [2, 17])

# Cross product
@pytest.mark.parametrize("x", [1, 2])
@pytest.mark.parametrize("y", [10, 20])
def test_multiply(x, y):
    assert x * y > 0
```

**Benefits:**
- Fewer test functions.
- Clearer failure messages.
- Easy to add new cases.

Python: What are Parametrized Tests and why use them?