Testing multiple exceptions in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of testing multiple exceptions in pytest?

To verify that a function or code block raises any one of several expected exceptions under different error conditions.

beginner

How do you test for multiple exceptions using pytest?

Use the pytest.raises() context manager with a tuple of exception types, like with pytest.raises((TypeError, ValueError)):.

beginner

What happens if the code inside pytest.raises() does not raise any exception?

The test fails because pytest expects an exception to be raised inside the with pytest.raises() block.

intermediate

Can you catch multiple exceptions separately in pytest tests?

Yes, but you write separate with pytest.raises() blocks for each exception to test them individually.

beginner

Example: How to test a function that may raise either ValueError or TypeError?

Use with pytest.raises((ValueError, TypeError)): and call the function inside this block to check if it raises either exception.

Which pytest syntax correctly tests for multiple exceptions?

A with pytest.raises(ValueError, TypeError):

B with pytest.raises(ValueError or TypeError):

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

D with pytest.raises[ValueError, TypeError]:

Use a tuple of exceptions inside pytest.raises(), like (ValueError, TypeError).

What happens if no exception is raised inside a pytest.raises() block?

A Test is ignored

B Test passes

C Test is skipped

D Test fails

pytest.raises expects an exception; if none is raised, the test fails.

How to test two different exceptions separately in pytest?

A Use one pytest.raises() with both exceptions

B Write two separate pytest.raises() blocks

C Use try-except inside the test

D Use assertRaises twice

Separate pytest.raises() blocks test each exception individually.

Which of these is NOT a valid exception to test with pytest.raises()?

A int

B TypeError

C KeyError

D ValueError

Only exception classes can be tested, not data types like int.

Why test multiple exceptions in one pytest.raises()?

A To check if any one of several errors occurs

B To catch all exceptions silently

C To ignore exceptions

D To speed up tests

Testing multiple exceptions ensures the code raises at least one expected error.

Explain how to use pytest to test that a function raises either ValueError or TypeError.

Think about how pytest.raises accepts multiple exceptions.

Describe what happens when no exception is raised inside a pytest.raises() block and why this is important.

Consider the purpose of testing exceptions.

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