Code coverage plugin in Cypress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a code coverage plugin in Cypress?

A code coverage plugin in Cypress helps measure how much of your application's code is tested by your tests. It shows which parts of the code ran during testing and which parts did not.

beginner

How does code coverage help improve software quality?

Code coverage helps identify untested parts of your code, so you can write tests for them. This reduces bugs and improves software reliability.

intermediate

Which file do you usually configure to enable the Cypress code coverage plugin?

You configure the code coverage plugin in the Cypress support file (usually cypress/support/e2e.js or e2e.ts) and the Cypress plugins file (cypress/plugins/index.js or index.ts).

intermediate

What is the role of the 'nyc' tool in Cypress code coverage?

'nyc' is a tool that collects and reports code coverage data. It works with Cypress to generate coverage reports showing which lines of code were tested.

beginner

Name one common file format used to store code coverage reports.

One common file format is 'lcov'. It is used to store detailed coverage data and can be viewed with many coverage report tools.

What does a code coverage plugin in Cypress measure?

A How fast the tests run

B Which parts of the code were executed during tests

C The number of tests written

D The size of the application code

Code coverage plugins measure which parts of the code were executed during tests to identify untested code.

Where do you add the code coverage plugin setup in a Cypress project?

A In the test spec files only

B In the package.json only

C In the Cypress support and plugins files

D In the node_modules folder

The setup for code coverage plugins is done in Cypress support and plugins files to hook into the test lifecycle.

Which tool is commonly used to generate code coverage reports with Cypress?

A nyc

B eslint

C webpack

D mocha

'nyc' is a popular tool to collect and generate code coverage reports.

What file format is often used to store detailed code coverage data?

A lcov

B json

C xml

D csv

'lcov' is a standard format for storing detailed code coverage information.

Why is code coverage important in testing?

A It automatically fixes bugs

B It speeds up test execution

C It reduces the size of the codebase

D It shows which code is tested and helps improve test completeness

Code coverage helps identify untested code, improving test completeness and software quality.

Explain how to set up a code coverage plugin in a Cypress project.

Think about installation, configuration files, and running tests.

Describe the benefits of using a code coverage plugin during testing.

Focus on quality and testing completeness.

Practice

1. What is the main purpose of the Cypress code coverage plugin?

easy

A. To show which parts of your code are tested and which are not

B. To speed up test execution time

C. To automatically fix bugs in your code

D. To generate user interface screenshots

Solution

1. Step 1: Understand code coverage concept

   Code coverage helps identify which lines or branches of code are executed during tests.

2. Step 2: Match purpose with plugin function

   The Cypress code coverage plugin tracks and reports tested vs untested code parts.

3. Final Answer:

   To show which parts of your code are tested and which are not -> Option A

4. Quick Check:

   Code coverage = tested vs untested code [OK]

Hint: Code coverage = shows tested and missed code parts [OK]

Common Mistakes:

• Thinking it speeds up tests
• Believing it fixes bugs automatically
• Confusing it with screenshot tools

2. Which file should you modify to enable the Cypress code coverage plugin support?

easy

A. cypress/support/e2e.js

B. cypress/fixtures/data.json

C. package.json

D. cypress.config.js

Solution

1. Step 1: Identify where plugin support code goes

   The plugin support code is added in the support file to load before tests run.

2. Step 2: Choose correct support file path

   By default, Cypress uses cypress/support/e2e.js for test support setup.

3. Final Answer:

   cypress/support/e2e.js -> Option A

4. Quick Check:

   Support file = cypress/support/e2e.js [OK]

Hint: Support code goes in cypress/support/e2e.js [OK]

Common Mistakes:

• Modifying cypress.config.js only
• Changing package.json for plugin support
• Editing fixture files for plugin setup

3. Given this snippet in cypress/support/e2e.js:

import '@cypress/code-coverage/support';

What will happen when you run your tests?

medium

A. Tests will fail due to missing plugin installation

B. No effect; code coverage requires config changes only

C. Code coverage data will be collected during tests

D. Tests will run but coverage report will be empty

Solution

1. Step 1: Understand import statement effect

   Importing '@cypress/code-coverage/support' enables coverage collection hooks.

2. Step 2: Recognize plugin behavior during test run

   This import activates coverage tracking so data is gathered as tests run.

3. Final Answer:

   Code coverage data will be collected during tests -> Option C

4. Quick Check:

   Import support = coverage data collected [OK]

Hint: Importing support enables coverage collection [OK]

Common Mistakes:

• Assuming import alone fails tests
• Thinking config changes alone enable coverage
• Believing coverage report is empty without extra steps

4. You added the code coverage plugin but your coverage report is empty after tests run. What is the most likely cause?

medium

A. You did not write any tests

B. You forgot to instrument your app code with the coverage tool

C. You imported the plugin support file twice

D. You ran tests in headless mode

Solution

1. Step 1: Understand coverage instrumentation

   Coverage requires your app code to be instrumented to track executed lines.

2. Step 2: Identify missing instrumentation effect

   Without instrumentation, coverage plugin cannot detect which code ran, so report is empty.

3. Final Answer:

   You forgot to instrument your app code with the coverage tool -> Option B

4. Quick Check:

   Missing instrumentation = empty coverage report [OK]

Hint: Instrument app code to get coverage data [OK]

Common Mistakes:

• Assuming no tests means empty report
• Thinking duplicate imports cause empty report
• Believing headless mode disables coverage

5. You want to improve your test suite by using the Cypress code coverage plugin. Which steps should you follow to get a working coverage report? Select the correct sequence.

hard

A. Instrument app code, run tests, install plugin, import support in e2e.js, check report

B. Run tests, install plugin, import support in e2e.js, instrument app code, check report

C. Import support in e2e.js, run tests, install plugin, instrument app code, check report

D. Install plugin, instrument app code, import support in e2e.js, run tests, check report

Solution

1. Step 1: Install the code coverage plugin

   First, add the plugin package to your project dependencies.

2. Step 2: Instrument your application code

   Modify your app build to include coverage instrumentation for tracking.

3. Step 3: Import the plugin support file in cypress/support/e2e.js

   This enables coverage hooks during test execution.

4. Step 4: Run your Cypress tests

   Tests will now collect coverage data as they execute.

5. Step 5: Check the generated coverage report

   Review which code was covered and improve tests accordingly.

6. Final Answer:

   Install plugin, instrument app code, import support in e2e.js, run tests, check report -> Option D

7. Quick Check:

   Correct setup sequence = Install plugin, instrument app code, import support in e2e.js, run tests, check report [OK]

Hint: Install, instrument, import support, run tests, check report [OK]

Common Mistakes:

• Running tests before installing plugin
• Skipping instrumentation step
• Importing support after running tests