How to Assert Equal in pytest: Simple Syntax and Examples

In pytest, you assert equality using the simple Python assert statement with the == operator, like assert actual == expected. Pytest automatically reports failures with detailed information when the assertion is false.

Syntax

The basic syntax to assert equality in pytest is:

• assert actual == expected: Checks if actual value equals expected value.
• If the assertion fails, pytest shows a clear error message with both values.

python

assert actual == expected

Example

This example shows a simple test function that checks if the sum of two numbers equals the expected result using assert.

python

def test_sum():
    result = 2 + 3
    expected = 5
    assert result == expected

Output

============================= test session starts =============================
collected 1 item

test_sample.py .                                                        [100%]

============================== 1 passed in 0.01s ==============================

Common Pitfalls

Common mistakes when asserting equality in pytest include:

• Using = instead of == (assignment vs comparison).
• Not understanding that assert is a Python keyword, not a pytest function.
• Comparing incompatible types that always fail.

python

def test_wrong_assert():
    value = 10
    # Wrong: assignment instead of comparison
    # assert value = 10  # SyntaxError

    # Correct:
    assert value == 10

Quick Reference

Tips for asserting equality in pytest:

• Use assert actual == expected for clear, readable tests.
• Pytest shows detailed error messages automatically on failure.
• Use descriptive variable names to make tests easy to understand.

Key Takeaways

Use Python's assert actual == expected to check equality in pytest.

Pytest provides clear failure messages without extra code.

Avoid using = instead of == in assertions.

Write simple, readable assertions for easy debugging.

Test functions must start with test_ for pytest to discover them.