Testing custom exceptions in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom exception in Python testing?

A custom exception is a user-defined error type created by subclassing the built-in Exception class. It helps to signal specific error conditions in your code.

beginner

How do you test that a custom exception is raised using pytest?

Use pytest.raises() as a context manager around the code that should raise the exception. Then assert the exception type matches your custom exception.

beginner

Example: Write a pytest snippet to check if MyError is raised when calling func().

import pytest

with pytest.raises(MyError):
    func()

intermediate

Why create custom exceptions instead of using built-in exceptions?

Custom exceptions make your error handling clearer and more specific. They help other developers understand what kind of error occurred and allow targeted exception handling.

intermediate

What is the benefit of checking the exception message in tests?

Checking the exception message ensures the error is not only the right type but also triggered for the expected reason, improving test accuracy.

Which pytest function is used to test if a custom exception is raised?

A pytest.expect()

B pytest.assertRaises()

C pytest.check_exception()

D pytest.raises()

pytest.raises() is the correct function to check if an exception is raised in pytest.

How do you define a custom exception in Python?

A exception MyError: pass

B def MyError(): pass

C class MyError(Exception): pass

D class MyError(): pass

Custom exceptions are defined by subclassing Exception, like 'class MyError(Exception): pass'.

What is the purpose of testing exception messages?

A To ignore the exception

B To verify the error reason is correct

C To improve test speed

D To check the exception type only

Testing messages confirms the exception was raised for the expected reason.

Which of these is NOT a benefit of custom exceptions?

A Automatically fixes bugs

B Clearer error handling

C More specific error types

D Easier debugging

Custom exceptions help with clarity and debugging but do not fix bugs automatically.

In pytest, what happens if the expected exception is NOT raised inside pytest.raises()?

A The test fails

B The test passes

C The test is skipped

D The test is ignored

If the expected exception is not raised, pytest.raises() causes the test to fail.

Explain how to write a pytest test that checks for a custom exception.

Think about how you catch errors in real life and how pytest helps you check for them.

Why is it useful to create and test custom exceptions in your code?

Consider how specific error messages help you fix problems faster.