Coverage reporting in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

Understanding coverage report output in Django tests

You run Django tests with coverage enabled. The coverage report shows 85% coverage for your app. What does this 85% mean?

A 85% of your app's database queries were tested.

B 85% of your test cases passed successfully.

C 85% of your Python code lines in the app were executed during tests.

D 85% of your app's HTML templates were rendered during tests.

💡 Hint

Think about what coverage tools measure: code execution, not test success or database queries.

Coverage percentage shows how many lines of your Python code ran during tests. It does not measure test success or database queries.

📝 Syntax

intermediate

Correct command to run Django tests with coverage

Which command correctly runs Django tests with coverage and generates an HTML report?

A coverage run manage.py test && coverage html

B python coverage run test manage.py && coverage html

C coverage test manage.py && coverage html

D python manage.py coverage test && coverage report

💡 Hint

Remember the order: coverage run runs a command, then coverage html generates the report.

The correct syntax is coverage run manage.py test to run tests with coverage, then coverage html to create the HTML report.

🔧 Debug

advanced

Why does coverage report show 0% after running Django tests?

You ran coverage run manage.py test but the coverage report shows 0% coverage. What is the most likely cause?

A Your tests passed too quickly for coverage to record data.

B Your tests did not import any code from your app.

C You forgot to install the coverage package.

D You ran tests without the coverage tool actually monitoring the code execution.

💡 Hint

Think about how coverage tracks code execution and what happens if it is not properly started.

If coverage is not properly started before running tests, it won't track code execution, resulting in 0% coverage.

❓ state_output

advanced

Interpreting coverage report details

After running coverage on your Django app, the report shows:

Name                  Stmts   Miss  Cover
-----------------------------------------
myapp/views.py           50     10    80%
myapp/models.py          30      0   100%
myapp/forms.py           20      5    75%

How many lines of code were missed in total?

A 15 lines missed

B 5 lines missed

C 10 lines missed

D 0 lines missed

💡 Hint

Add the missed lines from each file.

Missed lines are 10 + 0 + 5 = 15 total missed lines.

🧠 Conceptual

expert

Why exclude migrations from coverage reports in Django?

Why is it common to exclude migration files from coverage reports in Django projects?

A Because migrations are always 100% covered by default.

B Because migration files are auto-generated and not part of the app's logic to test.

C Because migrations run only in production, not during tests.

D Because coverage tools cannot read migration files.

💡 Hint

Think about what migrations are and why testing them is usually unnecessary.

Migrations are generated by Django to change the database schema. They are not hand-written logic and usually don't need coverage measurement.

Practice

1. What is the main purpose of coverage reporting in Django testing?

easy

A. To deploy the Django app to a server

B. To speed up the test execution

C. To automatically fix bugs in the code

D. To show which parts of your code are tested

Solution

1. Step 1: Understand coverage reporting

   Coverage reporting tracks which lines of code are executed during tests.

2. Step 2: Identify the main goal

   The goal is to see which parts of the code are covered by tests to improve test quality.

3. Final Answer:

   To show which parts of your code are tested -> Option D

4. Quick Check:

   Coverage shows tested code = A [OK]

Hint: Coverage shows tested code parts clearly [OK]

Common Mistakes:

• Thinking coverage speeds up tests
• Believing coverage fixes bugs automatically
• Confusing coverage with deployment

2. Which command correctly runs Django tests with coverage collection?

easy

A. coverage test manage.py run

B. python manage.py coverage test

C. coverage run manage.py test

D. manage.py coverage run test

Solution

1. Step 1: Recall the correct coverage command syntax

   The coverage tool runs the test command with: coverage run manage.py test

2. Step 2: Compare options

   Only coverage run manage.py test matches the correct syntax; others mix command order incorrectly.

3. Final Answer:

   coverage run manage.py test -> Option C

4. Quick Check:

   Correct coverage test command = A [OK]

Hint: Use 'coverage run' before 'manage.py test' [OK]

Common Mistakes:

• Swapping command order
• Using 'coverage test' instead of 'coverage run'
• Adding 'coverage' after manage.py

3. After running coverage run manage.py test, what command shows a summary of coverage results in the terminal?

medium

A. coverage report

B. coverage summary

C. coverage show

D. coverage list

Solution

1. Step 1: Identify the command for coverage summary

   The command to display coverage results in the terminal is 'coverage report'.

2. Step 2: Eliminate incorrect options

   Commands like 'coverage summary', 'coverage show', and 'coverage list' do not exist or do not show coverage summary.

3. Final Answer:

   coverage report -> Option A

4. Quick Check:

   Terminal coverage summary = coverage report = C [OK]

Hint: Use 'coverage report' to see terminal summary [OK]

Common Mistakes:

• Using non-existent commands like 'coverage summary'
• Confusing 'coverage html' with terminal report
• Trying 'coverage show' which is invalid

4. You ran coverage run manage.py test but coverage report shows 0% coverage. What is the likely cause?

medium

A. Coverage data file was deleted before report

B. Tests did not execute any code

C. Coverage was run without the test command

D. Coverage report command is misspelled

Solution

1. Step 1: Understand why coverage shows 0%

   If coverage data file is missing or deleted, report shows 0% coverage.

2. Step 2: Check other options

   Tests running but no coverage data means data file issue; misspelling report command causes error, not 0%.

3. Final Answer:

   Coverage data file was deleted before report -> Option A

4. Quick Check:

   Missing data file = 0% coverage = B [OK]

Hint: Check if .coverage file exists before report [OK]

Common Mistakes:

• Assuming tests never ran
• Thinking coverage run without test causes 0%
• Misspelling report causes error, not zero coverage

5. You want a detailed HTML report of your Django test coverage. Which sequence of commands should you run?

hard

A. coverage report && coverage run manage.py test

B. coverage run manage.py test && coverage html

C. coverage html && coverage run manage.py test

D. manage.py test coverage run && coverage report

Solution

1. Step 1: Run tests with coverage collection

   Use 'coverage run manage.py test' to collect coverage data while running tests.

2. Step 2: Generate HTML report

   Run 'coverage html' after tests to create a detailed HTML coverage report.

3. Step 3: Verify command order

   coverage run manage.py test && coverage html correctly chains these commands; others have wrong order or commands.

4. Final Answer:

   coverage run manage.py test && coverage html -> Option B

5. Quick Check:

   Run tests then html report = D [OK]

Hint: Run tests first, then 'coverage html' for report [OK]

Common Mistakes:

• Running 'coverage html' before tests
• Mixing command order
• Using 'manage.py test coverage run' which is invalid