Why coverage measures test completeness in PyTest - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the coverage module.

PyTest

import [1]

Drag options to blanks, or click blank then click option'

Acoverage

Bunittest

Cpytest

Dsys

Attempts:

3 left

💡 Hint

Common Mistakes

Importing pytest instead of coverage

Using unittest which is for testing but not coverage

The coverage module is used to measure how much of your code is tested.

2fill in blank

medium

Complete the code to start coverage measurement before tests.

PyTest

cov = coverage.Coverage()
cov.[1]()

Drag options to blanks, or click blank then click option'

Astop

Bstart

Crun

Dreport

Attempts:

3 left

💡 Hint

Common Mistakes

Calling stop() before tests

Using report() which is for showing results

We call start() to begin measuring coverage before running tests.

3fill in blank

hard

Fix the error in the code to stop coverage after tests.

PyTest

cov.[1]()

Drag options to blanks, or click blank then click option'

Aend

Bstart

Cbegin

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Calling start() again

Using non-existent methods like begin or end

After tests finish, we call stop() to end coverage measurement.

4fill in blank

hard

Fill both blanks to generate and save the coverage report.

PyTest

cov.[1]()
cov.[2]()

Drag options to blanks, or click blank then click option'

Areport

Bsave

Cstart

Dstop

Attempts:

3 left

💡 Hint

Common Mistakes

Calling start or stop instead of report or save

Reversing the order of methods

First, report() prints the coverage summary, then save() saves the data.

5fill in blank

hard

Fill all three blanks to run tests with coverage and print the report.

PyTest

cov = coverage.Coverage()
cov.[1]()
# run tests here
cov.[2]()
cov.[3]()

Drag options to blanks, or click blank then click option'

Astart

Bstop

Creport

Dsave

Attempts:

3 left

💡 Hint

Common Mistakes

Using save instead of report at the end

Stopping coverage before tests

We start coverage, run tests, stop coverage, then print the report.

Practice

1. What does test coverage measure in pytest?

easy

A. How much of the code is executed by tests

B. How many tests are written

C. How fast the tests run

D. How many errors tests find

Solution

1. Step 1: Understand the meaning of coverage

   Coverage shows which parts of the code are run when tests execute.

2. Step 2: Compare options to coverage definition

   Only How much of the code is executed by tests matches this meaning, others describe different test aspects.

3. Final Answer:

   How much of the code is executed by tests -> Option A

4. Quick Check:

   Coverage = executed code percentage [OK]

Hint: Coverage = code run by tests, not test count [OK]

Common Mistakes:

• Confusing coverage with number of tests
• Thinking coverage measures test speed
• Believing coverage counts errors found

2. Which pytest command correctly runs tests with coverage measurement?

easy

A. pytest --cover

B. pytest --coverage

C. pytest -cov-report

D. pytest --cov

Solution

1. Step 1: Recall pytest coverage plugin syntax

   The correct flag to measure coverage is '--cov'.

2. Step 2: Check options for correctness

   Only pytest --cov uses the exact correct flag '--cov'. Others are invalid or incomplete.

3. Final Answer:

   pytest --cov -> Option D

4. Quick Check:

   Use --cov to enable coverage [OK]

Hint: Use '--cov' flag to measure coverage in pytest [OK]

Common Mistakes:

• Using '--coverage' instead of '--cov'
• Mixing coverage report flags with coverage run flags
• Typing '--cover' which is invalid

3. Given this pytest coverage output:

Name          Stmts   Miss  Cover
my_module.py     10      2    80%

What does the 'Miss' number mean?

medium

A. Number of lines not executed by tests

B. Number of errors in code

C. Number of tests skipped

D. Number of tests that failed

Solution

1. Step 1: Understand coverage report columns

   'Miss' shows how many lines of code were not run by tests.

2. Step 2: Match 'Miss' meaning to options

   Number of lines not executed by tests correctly describes 'Miss' as unexecuted lines; others describe unrelated test results.

3. Final Answer:

   Number of lines not executed by tests -> Option A

4. Quick Check:

   Miss = untested lines count [OK]

Hint: 'Miss' means lines tests did not run [OK]

Common Mistakes:

• Thinking 'Miss' counts failed tests
• Confusing 'Miss' with skipped tests
• Assuming 'Miss' means code errors

4. You run pytest with coverage but get 0% coverage report. What is the most likely cause?

medium

A. Tests passed too quickly

B. Tests did not execute any code

C. Coverage plugin is not installed

D. Code has no functions

Solution

1. Step 1: Analyze 0% coverage meaning

   0% coverage means no code lines were run during tests.

2. Step 2: Evaluate causes

   If the coverage plugin is not installed, pytest will not measure coverage and may silently produce 0% coverage report or no coverage data.

3. Final Answer:

   Coverage plugin is not installed -> Option C

4. Quick Check:

   Missing plugin causes no coverage data [OK]

Hint: 0% coverage often means coverage plugin missing [OK]

Common Mistakes:

• Assuming plugin missing causes 0% without errors
• Thinking fast tests mean low coverage
• Believing code without functions can't be covered

5. You want to improve test completeness using coverage. Which approach is best?

hard

A. Write more tests without checking coverage

B. Add tests targeting uncovered code lines shown by coverage report

C. Ignore coverage and focus on test speed

D. Remove tests that run covered code

Solution

1. Step 1: Understand coverage report use

   Coverage shows which code lines lack tests, guiding where to add tests.

2. Step 2: Evaluate options for improving completeness

   Only Add tests targeting uncovered code lines shown by coverage report uses coverage data to add tests for uncovered code, improving completeness.

3. Final Answer:

   Add tests targeting uncovered code lines shown by coverage report -> Option B

4. Quick Check:

   Use coverage to find and test missing code [OK]

Hint: Add tests where coverage report shows gaps [OK]

Common Mistakes:

• Writing tests blindly without coverage info
• Ignoring coverage to focus on speed
• Removing tests that cover code