Testing multiple exceptions in PyTest - Build an Automation Script

Verify function raises correct exceptions for invalid inputs

Preconditions (2)

Step 1: Call 'process_input' with input that should raise ValueError

Step 2: Verify that ValueError is raised

Step 3: Call 'process_input' with input that should raise TypeError

Step 4: Verify that TypeError is raised

Step 5: Call 'process_input' with input that should raise KeyError

Step 6: Verify that KeyError is raised

✅ Expected Result: The function raises the expected exceptions for each invalid input

Automation Requirements - pytest

Assertions Needed:

Assert that ValueError is raised for invalid value input

Assert that TypeError is raised for invalid type input

Assert that KeyError is raised for missing key input

Best Practices:

Use pytest.raises context manager for exception testing

Write separate test functions or parameterize tests for clarity

Keep test code simple and readable

Automated Solution

PyTest

import pytest

# Example function to test

def process_input(data):
    if not isinstance(data, dict):
        raise TypeError("Input must be a dictionary")
    if 'key' not in data:
        raise KeyError("Missing 'key' in input")
    value = data['key']
    if value < 0:
        raise ValueError("Value must be non-negative")
    return value * 2


def test_process_input_raises_value_error():
    with pytest.raises(ValueError) as exc_info:
        process_input({'key': -1})
    assert str(exc_info.value) == "Value must be non-negative"


def test_process_input_raises_type_error():
    with pytest.raises(TypeError) as exc_info:
        process_input(['not', 'a', 'dict'])
    assert str(exc_info.value) == "Input must be a dictionary"


def test_process_input_raises_key_error():
    with pytest.raises(KeyError) as exc_info:
        process_input({'wrong_key': 10})
    assert str(exc_info.value) == "'Missing \'key\' in input'" or str(exc_info.value) == "'key'"

The code defines a sample function process_input that raises different exceptions based on input.

Each test function uses pytest.raises as a context manager to check for the expected exception.

Assertions check the exception message to ensure the correct error was raised.

This approach keeps tests clear and focused on one exception each, following best practices.

Common Mistakes - 3 Pitfalls

Not using pytest.raises and instead using try-except blocks manually

Catching too broad exceptions or multiple exceptions in one test without clarity

Not asserting the exception message

Bonus Challenge

Now add data-driven testing with 3 different invalid inputs to check all exceptions in one parameterized test

Show Hint