Testing multiple exceptions in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest test with multiple exception checks

What is the test result when running this pytest test function that checks for multiple exceptions?

PyTest

import pytest

def func(x):
    if x == 0:
        raise ValueError("Zero not allowed")
    elif x == 1:
        raise TypeError("One is wrong type")
    return x

def test_func_exceptions():
    with pytest.raises(ValueError):
        func(0)
    with pytest.raises(TypeError):
        func(1)

A Test passes but does not catch any exceptions.

B Test passes with both exceptions correctly caught.

C Test fails because only the first exception is caught; second raises an error.

D Test fails due to a SyntaxError in the test code.

💡 Hint

pytest.raises can be used multiple times in one test function to check different exceptions.

The test calls func with 0 and 1 inside separate pytest.raises blocks, so both exceptions are caught and the test passes.

❓ assertion

intermediate

Correct assertion to check multiple exceptions in pytest

Which assertion correctly tests that a function raises either ValueError or TypeError when called with certain inputs?

PyTest

def func(x):
    if x == 0:
        raise ValueError("Zero not allowed")
    elif x == 1:
        raise TypeError("One is wrong type")
    return x

A

with pytest.raises(ValueError):
    func(0)
with pytest.raises(TypeError):
    func(1)

B

with pytest.raises((ValueError, TypeError)):
    func(0)
    func(1)

C

with pytest.raises(ValueError) or pytest.raises(TypeError):
    func(0)
    func(1)

D assert func(0) raises ValueError and func(1) raises TypeError

💡 Hint

Use separate pytest.raises blocks for different exceptions.

Option A correctly uses separate pytest.raises blocks to check each exception individually. Option A incorrectly tries to catch both exceptions in one block but calls both functions inside it, which will fail on the first exception and not reach the second call.

🔧 Debug

advanced

Debug why second exception test is not reached

Why does the second exception test not run in this pytest code?

PyTest

import pytest

def func(x):
    if x == 0:
        raise ValueError("Zero not allowed")
    elif x == 1:
        raise TypeError("One is wrong type")
    return x

def test_func():
    with pytest.raises((ValueError, TypeError)):
        func(0)
        func(1)

A Because the test function is missing a return statement.

B Because pytest.raises cannot catch multiple exceptions in one block.

C Because func(1) does not raise any exception.

D Because func(0) raises ValueError and exits the with block before func(1) is called.

💡 Hint

Consider how exceptions interrupt code flow inside a with block.

When func(0) raises ValueError, the with block exits immediately, so func(1) is never called. To test both exceptions, separate with blocks are needed.

❓ framework

advanced

Best pytest pattern to test multiple exceptions separately

Which pytest test function correctly tests that func raises ValueError for 0 and TypeError for 1, ensuring both exceptions are tested independently?

PyTest

def func(x):
    if x == 0:
        raise ValueError("Zero not allowed")
    elif x == 1:
        raise TypeError("One is wrong type")
    return x

A

def test_func():
    with pytest.raises(ValueError):
        func(0)
    with pytest.raises(TypeError):
        func(1)

B

def test_func():
    with pytest.raises((ValueError, TypeError)):
        func(0)
        func(1)

C

def test_func():
    assert func(0) raises ValueError
    assert func(1) raises TypeError

D

def test_func():
    try:
        func(0)
    except ValueError:
        pass
    try:
        func(1)
    except TypeError:
        pass

💡 Hint

Use separate with blocks for each exception test.

Option A uses separate pytest.raises blocks, which is the recommended way to test multiple exceptions independently. Option A fails to test the second call because the first exception interrupts the block. Option A is invalid syntax. Option A does not use pytest's assertion mechanism and will not fail the test if exceptions are not raised.

🧠 Conceptual

expert

Why separate pytest.raises blocks are preferred for multiple exceptions

Why is it better to use separate pytest.raises blocks when testing multiple exceptions in one test function?

A Because combining exceptions in one block causes syntax errors.

B Because pytest.raises only supports one exception type per test file.

C Because each pytest.raises block stops execution on exception, so separate blocks ensure all exceptions are tested.

D Because pytest.raises automatically retries the block until all exceptions occur.

💡 Hint

Think about how exceptions affect code flow inside a with block.

Each pytest.raises block exits as soon as the expected exception is raised, so if multiple exceptions are tested in one block, only the first is caught. Separate blocks allow testing each exception independently.

Practice

1. What does pytest.raises((ValueError, TypeError)) do in a test?

easy

A. It passes if either ValueError or TypeError is raised during the test.

B. It passes only if both ValueError and TypeError are raised together.

C. It fails if any exception is raised during the test.

D. It ignores exceptions and always passes the test.

Solution

1. Step 1: Understand pytest.raises with tuple

   Using a tuple inside pytest.raises means the test expects any one of those exceptions.

2. Step 2: Effect on test pass/fail

   If the code raises either ValueError or TypeError, the test passes. If no exception or a different exception is raised, it fails.

3. Final Answer:

   It passes if either ValueError or TypeError is raised during the test. -> Option A

4. Quick Check:

   pytest.raises with tuple = any exception in tuple passes [OK]

Hint: Tuple in pytest.raises means any listed exception passes [OK]

Common Mistakes:

• Thinking both exceptions must be raised simultaneously
• Assuming it passes without exceptions
• Confusing tuple with multiple separate pytest.raises calls

2. Which of the following is the correct syntax to test for multiple exceptions in pytest?

easy

A. with pytest.raises{ValueError, TypeError}:

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

C. with pytest.raises([ValueError, TypeError]):

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

Solution

1. Step 1: Recall pytest.raises syntax

   pytest.raises expects a single exception or a tuple of exceptions inside parentheses.

2. Step 2: Identify correct tuple syntax

   Only with pytest.raises((ValueError, TypeError)): uses a tuple (parentheses with comma-separated exceptions) correctly.

3. Final Answer:

   with pytest.raises((ValueError, TypeError)): -> Option D

4. Quick Check:

   Tuple syntax with parentheses and comma = correct [OK]

Hint: Use parentheses and comma for multiple exceptions in pytest.raises [OK]

Common Mistakes:

• Using multiple arguments without tuple
• Using list brackets instead of tuple
• Using curly braces which are invalid syntax

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

def test_func():
    with pytest.raises((KeyError, IndexError)):
        d = {'a': 1}
        value = d['b']

medium

A. Test fails due to syntax error.

B. Test passes because KeyError is raised.

C. Test passes because IndexError is raised.

D. Test fails because no exception is raised.

Solution

1. Step 1: Identify exception raised by d['b']

   Accessing a missing key in a dictionary raises KeyError.

2. Step 2: Check if KeyError is in the tuple

   KeyError is in (KeyError, IndexError), so pytest.raises expects it and test passes.

3. Final Answer:

   Test passes because KeyError is raised. -> Option B

4. Quick Check:

   Missing dict key = KeyError, in tuple = pass [OK]

Hint: Missing dict key raises KeyError, matches tuple exceptions [OK]

Common Mistakes:

• Thinking IndexError is raised instead
• Assuming no exception is raised
• Confusing KeyError with ValueError

4. What will be the result of this pytest test?

def test_divide():
    with pytest.raises((ZeroDivisionError, ValueError)):
        result = 10 / 0
        int('abc')

medium

A. The test will pass because ZeroDivisionError is raised first.

B. The test will fail because the second line after exception is unreachable.

C. The test will fail because only ZeroDivisionError is raised, not ValueError.

D. The test will fail due to syntax error in pytest.raises.

Solution

1. Step 1: Analyze exception flow in with block

   ZeroDivisionError occurs at 10 / 0, so the next line int('abc') is never executed.

2. Step 2: Understand pytest.raises behavior

   ZeroDivisionError is in the expected tuple, so test passes. ValueError is unreachable.

3. Step 3: Confirm test outcome

   Since a matching exception (ZeroDivisionError) is raised first, the test passes.

4. Final Answer:

   The test will pass because ZeroDivisionError is raised first. -> Option A

5. Quick Check:

   Exception stops code, later lines unreachable; matching exc = pass [OK]

Hint: Exception stops code; lines after are not run [OK]

Common Mistakes:

• Thinking both exceptions must be raised simultaneously
• Thinking test fails due to syntax
• Ignoring unreachable code after exception

5. You want to test a function that can raise either IndexError or KeyError depending on input. Which pytest test code correctly checks both exceptions in one test?

hard

A. def test_func():
with pytest.raises(IndexError, KeyError):
func_that_raises()

B. def test_func():
with pytest.raises([IndexError, KeyError]):
func_that_raises()

C. def test_func():
with pytest.raises((IndexError, KeyError)):
func_that_raises()

D. def test_func():
with pytest.raises({IndexError, KeyError}):
func_that_raises()

Solution

1. Step 1: Recall correct syntax for multiple exceptions

   pytest.raises expects a tuple of exceptions to check multiple exceptions in one block.

2. Step 2: Identify correct tuple usage

   def test_func(): with pytest.raises((IndexError, KeyError)): func_that_raises() uses a tuple (parentheses with comma-separated exceptions), which is correct syntax.

3. Step 3: Check other options

   Options A, B, and D use invalid syntax: multiple arguments without tuple, list, or set instead of tuple.

4. Final Answer:

   def test_func(): with pytest.raises((IndexError, KeyError)): func_that_raises() -> Option C

5. Quick Check:

   Tuple of exceptions in pytest.raises = correct [OK]

Hint: Use tuple (parentheses, commas) for multiple exceptions in pytest.raises [OK]

Common Mistakes:

• Passing exceptions as separate arguments
• Using list or set instead of tuple
• Forgetting parentheses around exceptions