Subprocess testing in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is subprocess testing in software testing?

Subprocess testing checks how a program runs other programs or commands outside itself. It ensures these external calls work correctly.

beginner

Which Python module is commonly used to run subprocesses in tests?

The subprocess module lets Python code start and control other programs. It is often used in subprocess testing.

intermediate

How can you check the output of a subprocess in pytest?

Use subprocess.run() with capture_output=True to get the output. Then assert the output matches expected results.

intermediate

Why should subprocess calls be mocked in unit tests?

Mocking subprocess calls avoids running real commands, which can be slow or unsafe. It helps tests run fast and reliably.

advanced

What is a good practice for locating subprocess commands in tests?

Use absolute paths or environment variables to locate commands. This avoids errors from missing or wrong commands during tests.

Which function runs a subprocess and waits for it to finish in Python?

A subprocess.execute()

B subprocess.start()

C subprocess.run()

D subprocess.call_async()

subprocess.run() runs a command and waits for it to complete, returning a result object.

In pytest, how do you capture the output of a subprocess?

A Use <code>capture_output=True</code> in <code>subprocess.run()</code>

B Use <code>print()</code> inside the subprocess

C Use <code>subprocess.output()</code>

D Use <code>subprocess.capture()</code>

Setting capture_output=True captures stdout and stderr for assertions.

Why mock subprocess calls in unit tests?

A To skip testing subprocess behavior

B To avoid running real commands that may be slow or unsafe

C To make tests run slower

D To run commands twice

Mocking prevents side effects and speeds up tests.

What does subprocess.CompletedProcess contain?

A Only the process ID

B The environment variables

C The source code of the subprocess

D Return code, stdout, and stderr of the subprocess

This object holds the result details after subprocess finishes.

Which is a best practice for subprocess command paths in tests?

A Use absolute paths or environment variables

B Use relative paths without checking

C Hardcode commands without paths

D Ignore command locations

Absolute paths avoid errors from missing or wrong commands.

Explain how to test a subprocess call using pytest, including capturing output and making assertions.

Think about how to run the command and check what it prints or returns.

Describe why and how you would mock subprocess calls in unit tests.

Consider the risks of running real commands during tests.