Testing custom exceptions in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest test for custom exception

What is the test result when running this pytest code that checks for a custom exception?

PyTest

import pytest

class MyError(Exception):
    pass

def func():
    raise MyError("fail")

def test_func_raises():
    with pytest.raises(MyError):
        func()

A Test fails with MyError uncaught

B Test fails with AssertionError

C Test passes with no errors

D Test raises TypeError during execution

💡 Hint

pytest.raises expects the specified exception to be raised inside the with block.

The test passes because func() raises MyError as expected, so pytest.raises catches it and the test succeeds.

❓ assertion

intermediate

Correct assertion to test exception message

Which assertion correctly tests that the exception message contains the word 'timeout'?

PyTest

import pytest

def func():
    raise TimeoutError("Connection timeout occurred")

def test_func():
    with pytest.raises(TimeoutError) as exc_info:
        func()
    # Which assertion below is correct here?

A assert exc_info.value.args[0] == 'timeout'

B assert 'timeout' in str(exc_info.value)

C assert exc_info.value.message == 'timeout'

D assert exc_info.message == 'timeout'

💡 Hint

Exception message is accessed by converting exc_info.value to string.

The exception message is stored in exc_info.value and converting it to string shows the message. The other options access non-existent attributes or expect exact match.

🔧 Debug

advanced

Identify the error in this pytest exception test

Why does this pytest test fail with an error instead of passing?

PyTest

import pytest

class CustomError(Exception):
    pass

def func():
    raise CustomError("error")

def test_func():
    with pytest.raises(CustomError):
        func

A func is referenced without parentheses, so exception is never raised

B pytest.raises expects a string, not an exception class

C CustomError is not derived from Exception

D The exception message must be checked inside pytest.raises

💡 Hint

Check how func is called inside the with block.

The test fails because func is referenced but not called (missing parentheses), so no exception is raised and pytest.raises fails.

🧠 Conceptual

advanced

Why use custom exceptions in testing?

What is the main advantage of defining and testing custom exceptions in your code?

A They make the code run faster by skipping error checks

B They automatically fix bugs without extra code

C They reduce the need for writing test cases

D They allow more precise error handling and clearer test failure reasons

💡 Hint

Think about how custom exceptions help in identifying specific problems.

Custom exceptions help identify specific error conditions clearly, making tests more precise and easier to understand.

❓ framework

expert

Best pytest pattern for testing multiple custom exceptions

You want to test that a function raises either CustomErrorA or CustomErrorB depending on input. Which pytest pattern correctly tests this in one test function?

A Use pytest.raises with a tuple of exceptions: with pytest.raises((CustomErrorA, CustomErrorB)): func(x)

B Write two separate test functions, each with pytest.raises for one exception

C Use try-except inside the test and assert exception type manually

D Use pytest.raises with a list of exceptions: with pytest.raises([CustomErrorA, CustomErrorB]): func(x)

💡 Hint

Check pytest documentation for multiple exceptions in raises.

pytest.raises accepts a tuple of exception classes to check for multiple possible exceptions in one test.