Running tests (pytest command) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of pytest with a failing test

What will be the output summary when running pytest on the following test file containing one passing and one failing test?

PyTest

def test_pass():
    assert 1 == 1

def test_fail():
    assert 2 == 3

A 2 passed in 0.01s

B 1 failed in 0.01s

C 1 passed, 1 failed in 0.01s

D No tests collected

💡 Hint

pytest reports the number of tests passed and failed after running.

pytest runs both tests. One passes, one fails, so the summary shows '1 passed, 1 failed'.

❓ assertion

intermediate

Correct assertion to check a function raises an exception

Which pytest assertion correctly tests that calling function foo() raises a ValueError?

PyTest

def foo():
    raise ValueError('error')

A assert foo() == ValueError

B

with pytest.raises(ValueError):
    foo()

C assert foo() raises ValueError

D assert foo() throws ValueError

💡 Hint

pytest has a special context manager for checking exceptions.

pytest.raises is the correct way to assert exceptions in pytest. Other options are invalid syntax or incorrect.

🔧 Debug

advanced

Why does pytest not discover tests in this file?

Given this test file named test_sample.py, pytest does not find any tests. Why?

PyTest

def sample_test():
    assert True

A Test function name does not start with 'test_'

B Function has no parameters

C Missing import pytest statement

D File name should not start with 'test_'

💡 Hint

pytest discovers tests by function name patterns.

pytest only discovers functions starting with 'test_'. 'sample_test' does not match, so no tests found.

❓ framework

advanced

How to run pytest with detailed output and stop after first failure

Which pytest command runs tests showing detailed info and stops after the first failure?

A pytest -q --maxfail=0

B pytest --maxfail=1 --quiet

C pytest --stop-on-failure --verbose

D pytest -v -x

💡 Hint

Check pytest options for verbosity and stopping on failure.

-v is verbose, -x stops after first failure. Other options are invalid or contradictory.

🧠 Conceptual

expert

Understanding pytest fixture scope impact on test runs

If a pytest fixture has scope='module', how many times is it set up and torn down when running 5 tests in the same module?

A Setup once before all 5 tests, teardown once after all tests

B Setup and teardown before and after each test (5 times each)

C Setup and teardown twice, splitting tests into groups

D Setup once before first test, teardown after third test

💡 Hint

Fixture scope controls how often setup/teardown runs.

Module scope means fixture runs once per module, so setup and teardown happen once for all tests in that module.

Practice

1. What does the basic pytest command do when run in a project folder?

easy

A. It only checks the syntax of test files without running them.

B. It automatically finds and runs all test files and test functions.

C. It deletes all test files in the folder.

D. It installs pytest in the project folder.

Solution

1. Step 1: Understand the default behavior of pytest command

   Running pytest without arguments searches for test files and runs all tests found.

2. Step 2: Eliminate incorrect options

   Options A, C, and D describe actions pytest does not perform by default.

3. Final Answer:

   It automatically finds and runs all test files and test functions. -> Option B

4. Quick Check:

   pytest runs tests automatically = B [OK]

Hint: pytest runs all tests by default when no file is specified [OK]

Common Mistakes:

• Thinking pytest only checks syntax
• Assuming pytest deletes files
• Confusing pytest with package installer

2. Which of the following is the correct command to run pytest with detailed output?

easy

A. pytest -v

B. pytest --detail

C. pytest -d

D. pytest --verbose-output

Solution

1. Step 1: Recall pytest option for verbose output

   The -v option stands for verbose and shows detailed test results.

2. Step 2: Check other options for correctness

   Options -d, --detail, and --verbose-output are not valid pytest flags.

3. Final Answer:

   pytest -v -> Option A

4. Quick Check:

   Verbose flag is -v = C [OK]

Hint: Use -v for verbose pytest output [OK]

Common Mistakes:

• Using -d instead of -v
• Typing long incorrect flags
• Confusing verbose with debug flags

3. Given the command pytest test_math.py, what will happen?

medium

A. pytest runs all tests in all files in the folder.

B. pytest runs tests but ignores test_math.py.

C. pytest runs only the tests inside the file named test_math.py.

D. pytest runs tests only if they are named test_math.py inside any folder.

Solution

1. Step 1: Understand pytest file argument behavior

   When a filename is given, pytest runs tests only from that file.

2. Step 2: Eliminate incorrect options

   A: Runs all tests in all files (wrong when file specified). B: Ignores test_math.py (wrong). C: Misunderstands filename as test name search (wrong).

3. Final Answer:

   pytest runs only the tests inside the file named test_math.py. -> Option C

4. Quick Check:

   pytest filename runs tests in that file only = D [OK]

Hint: Specify filename to run tests only from that file [OK]

Common Mistakes:

• Assuming pytest runs all tests ignoring filename
• Confusing filename with test function name
• Thinking pytest ignores specified files

4. You run pytest -v test_example.py but get an error: pytest: error: unrecognized arguments: -v. What is the likely cause?

medium

A. pytest does not support the -v option.

B. You typed the option incorrectly; it should be --verbose.

C. The test file test_example.py does not exist.

D. You are running pytest with a wrong command or from a wrong environment.

Solution

1. Step 1: Understand the error message

   The error says -v is unrecognized, which is unusual because -v is a valid pytest option.

2. Step 2: Identify environment or command issues

   This usually means pytest is not properly installed or a different command is running (like python or another tool).

3. Final Answer:

   You are running pytest with a wrong command or from a wrong environment. -> Option D

4. Quick Check:

   Unrecognized option means wrong environment = A [OK]

Hint: Check pytest installation and environment if options fail [OK]

Common Mistakes:

• Assuming -v is invalid option
• Ignoring environment issues
• Blaming test file existence for option errors

5. You want to run only tests marked as slow in your project using pytest. Which command correctly runs only those tests?

hard

A. pytest -m slow

B. pytest --only slow

C. pytest --mark slow

D. pytest -s slow

Solution

1. Step 1: Recall pytest marker option

   The -m option runs tests matching a marker expression, such as slow.

2. Step 2: Verify other options

   Options --only, --mark, and -s do not filter tests by marker.

3. Final Answer:

   pytest -m slow -> Option A

4. Quick Check:

   Use -m to run tests by marker = A [OK]

Hint: Use -m marker to run tests with that marker [OK]

Common Mistakes:

• Using incorrect flags like --only or --mark
• Confusing -s (capture output) with marker filtering
• Not marking tests before filtering