Running tests (pytest command) - Build an Automation Script

Run pytest tests and verify output

Preconditions (3)

Step 1: Open a terminal or command prompt

Step 2: Navigate to the directory containing test_sample.py

Step 3: Run the command: pytest

Step 4: Observe the test execution output in the terminal

✅ Expected Result: pytest runs all tests in test_sample.py and shows a summary with number of tests passed or failed

Automation Requirements - pytest

Assertions Needed:

Verify that pytest command runs without errors

Verify that the test output contains '1 passed' for the sample test

Best Practices:

Use assert statements inside test functions

Keep test files and functions named with 'test_' prefix

Run pytest from the command line in the correct directory

Automated Solution

PyTest

import subprocess
import sys

def test_run_pytest_command():
    # Run pytest command on test_sample.py
    result = subprocess.run([sys.executable, '-m', 'pytest', 'test_sample.py'], capture_output=True, text=True)
    # Check that pytest exited with code 0 (success)
    assert result.returncode == 0, f"pytest failed with code {result.returncode}"
    # Check output contains '1 passed' indicating one test passed
    assert '1 passed' in result.stdout, "Expected '1 passed' in pytest output"

This test runs the pytest command on the test_sample.py file using Python's subprocess module.

We capture the output and check the return code to ensure pytest ran successfully.

Then we assert that the output contains '1 passed' which means one test passed as expected.

This simulates running pytest from the command line and verifies the test execution result.

Common Mistakes - 3 Pitfalls

Not capturing output from the pytest command

Running pytest without specifying the test file or directory

Not checking the return code of the pytest command

Bonus Challenge

Now add data-driven testing by running pytest on three different test files and verify each output

Show Hint

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