pytest.raises context manager - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest.raises with ZeroDivisionError

What will be the output of this test code when run with pytest?

PyTest

import pytest

def test_division():
    with pytest.raises(ZeroDivisionError):
        x = 1 / 0
    print("Test passed")

A No output because test is skipped

B ZeroDivisionError is raised and test fails

C SyntaxError due to incorrect pytest usage

D Test passed

💡 Hint

pytest.raises expects the code inside to raise the specified error to pass.

The code inside the with block raises ZeroDivisionError, which pytest.raises catches, so the test passes and prints 'Test passed'.

❓ assertion

intermediate

Correct assertion to check exception message with pytest.raises

Which option correctly asserts that a ValueError with message 'invalid input' is raised?

PyTest

import pytest

def func():
    raise ValueError('invalid input')

def test_func():
    with pytest.raises(ValueError) as excinfo:
        func()
    # Which assertion below is correct?

A assert excinfo.value.message == 'invalid input'

B assert excinfo.message == 'invalid input'

C assert 'invalid input' in str(excinfo.value)

D assert excinfo == 'invalid input'

💡 Hint

Exception message is accessed via str(excinfo.value).

The exception message is stored in excinfo.value and converted to string with str(). The other options access non-existent attributes.

🔧 Debug

advanced

Why does this pytest.raises test fail?

Given this test code, why does pytest report a failure?

PyTest

import pytest

def test_error():
    with pytest.raises(ValueError):
        x = int('abc')
    with pytest.raises(TypeError):
        x = int('abc')

A The first with block does not raise any error

B The second with block expects TypeError but int('abc') raises ValueError

C pytest.raises cannot be used twice in one test

D int('abc') raises SyntaxError, not ValueError or TypeError

💡 Hint

Check the actual error type raised by int('abc').

int('abc') raises ValueError, so the first with block passes but the second expects TypeError and fails.

🧠 Conceptual

advanced

Behavior of pytest.raises when no exception is raised

What happens if the code inside a pytest.raises context manager does NOT raise the expected exception?

A The test fails with Failed: DID NOT RAISE <ExceptionType>

B The test passes silently

C pytest.raises raises a SyntaxError

D The test is skipped automatically

💡 Hint

pytest.raises expects an exception to be raised inside the block.

If no exception is raised, pytest.raises causes the test to fail with a message indicating the expected exception was not raised.

❓ framework

expert

Using pytest.raises to test multiple exception types

Which option correctly tests that a function raises either ValueError or TypeError using pytest.raises?

A

with pytest.raises((ValueError, TypeError)):
    func()

B

with pytest.raises(ValueError | TypeError):
    func()

C

with pytest.raises(ValueError) and pytest.raises(TypeError):
    func()

D

with pytest.raises(ValueError) or pytest.raises(TypeError):
    func()

💡 Hint

pytest.raises accepts a tuple of exception types to check multiple exceptions.

pytest.raises accepts a tuple of exceptions to check if any of them is raised. The other options are invalid syntax or logic.

Practice

1. What is the main purpose of using pytest.raises in a test?

easy

A. To skip a test when an error occurs

B. To check if a specific error is raised by the code inside the block

C. To automatically fix errors in the tested code

D. To print error messages during test execution

Solution

1. Step 1: Understand the role of pytest.raises

   pytest.raises is used to verify that a certain error is raised when running code inside its context.

2. Step 2: Compare options with this purpose

   Only To check if a specific error is raised by the code inside the block correctly states that pytest.raises checks for expected errors. Other options describe unrelated behaviors.

3. Final Answer:

   To check if a specific error is raised by the code inside the block -> Option B

4. Quick Check:

   pytest.raises checks errors = A [OK]

Hint: Remember: pytest.raises expects an error inside its with block [OK]

Common Mistakes:

• Thinking pytest.raises fixes errors automatically
• Confusing pytest.raises with test skipping
• Using pytest.raises to print errors

2. Which of the following is the correct syntax to use pytest.raises to check for a ValueError?

easy

A. with pytest.raises(ValueError):\n function_call()

B. pytest.raises(ValueError):\nfunction_call()

C. with pytest.raises('ValueError'):\n function_call()

D. pytest.raises(ValueError)\n function_call()

Solution

1. Step 1: Recall correct context manager syntax

   pytest.raises must be used with the with keyword and the exception class without quotes.

2. Step 2: Evaluate each option

   with pytest.raises(ValueError):\n function_call() correctly uses with pytest.raises(ValueError):. Options A and B miss the with keyword. with pytest.raises('ValueError'):\n function_call() incorrectly uses quotes around the exception.

3. Final Answer:

   with pytest.raises(ValueError):\n function_call() -> Option A

4. Quick Check:

   Use with + exception class (no quotes) = D [OK]

Hint: Always use 'with' and exception class without quotes [OK]

Common Mistakes:

• Omitting the 'with' keyword
• Putting exception name in quotes
• Not indenting code inside the block

3. What will be the result of this test code?

import pytest

def test_divide():
    with pytest.raises(ZeroDivisionError):
        x = 1 / 0

medium

A. Test fails because no error is raised

B. Test passes but warns about division

C. Test fails due to syntax error

D. Test passes because ZeroDivisionError is raised

Solution

1. Step 1: Analyze the code inside pytest.raises

   The code divides 1 by 0, which raises a ZeroDivisionError as expected.

2. Step 2: Understand pytest.raises behavior

   Since the expected error occurs, pytest.raises catches it and the test passes.

3. Final Answer:

   Test passes because ZeroDivisionError is raised -> Option D

4. Quick Check:

   Expected error raised = test passes = B [OK]

Hint: If expected error occurs inside with block, test passes [OK]

Common Mistakes:

• Thinking test fails when error is raised
• Confusing ZeroDivisionError with other exceptions
• Assuming syntax error without checking code

4. Identify the error in this test code using pytest.raises:

import pytest

def test_key_error():
    with pytest.raises(KeyError):
    d = {'a': 1}
    x = d['b']

medium

A. Indentation error inside the with block

B. Wrong exception type used

C. Missing import of pytest

D. No error; code is correct

Solution

1. Step 1: Check indentation inside the with block

   The lines inside the with block must be indented. Here, d = {'a': 1} and x = d['b'] are not indented properly.

2. Step 2: Verify other aspects

   pytest is imported, and KeyError is the correct exception for missing key access. So no other errors.

3. Final Answer:

   Indentation error inside the with block -> Option A

4. Quick Check:

   Indent code inside with block = C [OK]

Hint: Indent all code inside the with block properly [OK]

Common Mistakes:

• Not indenting code inside the with block
• Using wrong exception type
• Forgetting to import pytest

5. You want to test a function parse_int(s) that should raise ValueError when given a non-integer string. Which of these test snippets correctly uses pytest.raises to check this behavior and also verifies the error message contains 'invalid'?

hard

A. with pytest.raises('ValueError') as e:
parse_int('abc')
assert 'invalid' in e

B. with pytest.raises(ValueError):
parse_int('abc')
assert 'invalid' in str(ValueError)

C. with pytest.raises(ValueError) as excinfo:
parse_int('abc')
assert 'invalid' in str(excinfo.value)

D. pytest.raises(ValueError):
parse_int('abc')
assert 'invalid' in str(excinfo.value)

Solution

1. Step 1: Use pytest.raises as context manager with 'as' to capture exception info

   with pytest.raises(ValueError) as excinfo: parse_int('abc') assert 'invalid' in str(excinfo.value) correctly uses as excinfo to capture the exception object for later inspection.

2. Step 2: Check the error message from excinfo.value

   with pytest.raises(ValueError) as excinfo: parse_int('abc') assert 'invalid' in str(excinfo.value) asserts that 'invalid' is in the string form of the exception value, which is the correct way to check the error message.

3. Final Answer:

   with pytest.raises(ValueError) as excinfo: parse_int('abc') assert 'invalid' in str(excinfo.value) -> Option C

4. Quick Check:

   Use 'as excinfo' and check excinfo.value message = A [OK]

Hint: Use 'as excinfo' to check error message inside pytest.raises [OK]

Common Mistakes:

• Putting exception name in quotes
• Not capturing exception info with 'as'
• Checking error message outside the context incorrectly