Docker execution in Cypress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main benefit of running Cypress tests inside a Docker container?

Running Cypress tests in Docker ensures a consistent environment across different machines, avoiding "it works on my machine" problems.

beginner

Which Docker command is used to start a container and run Cypress tests inside it?

The command docker run is used to start a container and execute Cypress tests inside it.

intermediate

Why should you mount your project directory as a volume when running Cypress in Docker?

Mounting your project directory as a volume allows Cypress inside the container to access your test files and code changes without rebuilding the image.

beginner

What is the purpose of the cypress/included Docker image?

The cypress/included image comes pre-installed with Cypress and all dependencies, making it easy to run tests without extra setup.

intermediate

How can you view Cypress test results when running tests inside Docker?

You can view test results by configuring Cypress to output reports to a mounted folder or by using the Docker logs command to see console output.

Which Docker option allows you to share your local test files with the container running Cypress?

A -v (volume mount)

B -p (port mapping)

C -d (detached mode)

D -e (environment variable)

The -v option mounts a local directory into the container, sharing files.

What does the cypress/included Docker image provide?

A Only Cypress CLI without dependencies

B A Cypress image for building custom plugins

C A base Linux image without Cypress

D Cypress pre-installed with all dependencies

The cypress/included image includes Cypress and all needed dependencies ready to run tests.

Why is Docker useful for running Cypress tests in CI/CD pipelines?

A It replaces the need for writing tests

B It speeds up test execution by using GPUs

C It provides a consistent environment for tests

D It automatically fixes test failures

Docker ensures tests run in the same environment every time, avoiding environment-related failures.

Which command runs Cypress tests inside a Docker container interactively?

A docker run -it cypress/included:latest

B docker build -t cypress-test .

C docker ps -a

D docker stop cypress

The docker run -it command runs the container interactively, useful for Cypress test execution.

How can you pass environment variables to Cypress tests in Docker?

A By mounting a volume with variables

B Using the <code>-e</code> flag with <code>docker run</code>

C By editing the Dockerfile only

D By running Cypress outside Docker

The -e flag sets environment variables inside the container for Cypress to use.

Explain how to set up and run Cypress tests inside a Docker container from scratch.

Think about the Docker image, volume mounting, and running commands.

Describe the advantages of using Docker for Cypress test execution in a team environment.

Focus on environment consistency and ease of sharing.

Practice

1. What is the main benefit of running Cypress tests inside a Docker container?

easy

A. It provides a clean and consistent environment for tests.

B. It makes tests run faster on all machines.

C. It automatically fixes test failures.

D. It removes the need for writing test code.

Solution

1. Step 1: Understand Docker's role in testing

   Docker creates isolated environments that are the same everywhere.

2. Step 2: Connect Docker benefits to Cypress tests

   Running Cypress in Docker ensures tests run in a clean, consistent setup, avoiding environment differences.

3. Final Answer:

   It provides a clean and consistent environment for tests. -> Option A

4. Quick Check:

   Docker = consistent test environment [OK]

Hint: Docker ensures same environment everywhere for tests [OK]

Common Mistakes:

• Thinking Docker speeds up tests automatically
• Believing Docker fixes test code errors
• Assuming Docker removes need for tests

2. Which Docker command correctly runs Cypress tests mounting the current folder as a volume?

easy

A. docker run -v $(pwd):/e2e -w /e2e cypress/included:12.0.0

B. docker run -p 8080:80 cypress/included:12.0.0

C. docker build -t cypress-test .

D. docker run cypress/included:12.0.0 --no-volume

Solution

1. Step 1: Identify volume mounting syntax

   The -v option mounts a folder; $(pwd):/e2e mounts current folder to /e2e in container.

2. Step 2: Check command correctness

   docker run -v $(pwd):/e2e -w /e2e cypress/included:12.0.0 uses -v and -w to set working directory, which is correct for running Cypress tests.

3. Final Answer:

   docker run -v $(pwd):/e2e -w /e2e cypress/included:12.0.0 -> Option A

4. Quick Check:

   Volume mount = -v [OK]

Hint: Use -v to mount volumes in Docker run command [OK]

Common Mistakes:

• Using -p instead of -v for volume mounting
• Forgetting to set working directory with -w
• Confusing docker build with docker run

3. Given this Docker command:

docker run -v $(pwd):/e2e -w /e2e cypress/included:12.0.0

What will happen if your current folder has no Cypress tests?

medium

A. Docker will throw a syntax error and stop.

B. The container will fail to start due to missing tests.

C. Cypress will automatically create sample tests.

D. The container will run but no tests will execute.

Solution

1. Step 1: Understand volume mounting effect

   The current folder is mounted inside the container at /e2e, so container sees the files you have.

2. Step 2: Consider what happens with no tests

   If no test files exist, Cypress runs but finds nothing to execute, so no tests run but container runs fine.

3. Final Answer:

   The container will run but no tests will execute. -> Option D

4. Quick Check:

   No tests = no execution, container still runs [OK]

Hint: No tests means no runs, but container still starts [OK]

Common Mistakes:

• Expecting Docker syntax error for missing files
• Thinking Cypress auto-generates tests
• Assuming container fails to start without tests

4. You run Cypress tests in Docker but see this error:
ERROR: Cannot find module 'cypress'
What is the most likely cause?

medium

A. You forgot to mount your test folder with node_modules.

B. You used the wrong Docker image without Cypress installed.

C. Your Dockerfile syntax is incorrect.

D. Your tests have syntax errors.

Solution

1. Step 1: Analyze the error message

   The error says Cypress module is missing, meaning Cypress is not installed in the container.

2. Step 2: Check Docker image used

   If you use a Docker image without Cypress pre-installed, this error occurs. Using cypress/included images avoids this.

3. Final Answer:

   You used the wrong Docker image without Cypress installed. -> Option B

4. Quick Check:

   Missing module = wrong image [OK]

Hint: Use official cypress/included image to avoid missing Cypress [OK]

Common Mistakes:

• Blaming test syntax errors for missing module
• Assuming volume mount fixes missing Cypress
• Confusing Dockerfile syntax with missing module

5. You want to run Cypress tests in Docker and save screenshots and videos outside the container. Which command correctly achieves this?

hard

A. docker run -p 8080:80 -v $(pwd):/e2e cypress/included:12.0.0

B. docker run -v $(pwd):/e2e -w /e2e cypress/included:12.0.0 --save-artifacts

C. docker run -v $(pwd):/e2e -v $(pwd)/cypress/screenshots:/e2e/cypress/screenshots -v $(pwd)/cypress/videos:/e2e/cypress/videos -w /e2e cypress/included:12.0.0

D. docker run --rm cypress/included:12.0.0

Solution

1. Step 1: Understand volume mounting for artifacts

   To save screenshots and videos outside Docker, mount their folders as volumes from host to container.

2. Step 2: Check command for multiple volume mounts

   docker run -v $(pwd):/e2e -v $(pwd)/cypress/screenshots:/e2e/cypress/screenshots -v $(pwd)/cypress/videos:/e2e/cypress/videos -w /e2e cypress/included:12.0.0 mounts the whole project plus screenshots and videos folders separately, ensuring artifacts persist on host.

3. Final Answer:

   docker run -v $(pwd):/e2e -v $(pwd)/cypress/screenshots:/e2e/cypress/screenshots -v $(pwd)/cypress/videos:/e2e/cypress/videos -w /e2e cypress/included:12.0.0 -> Option C

4. Quick Check:

   Mount artifact folders to save outside container [OK]

Hint: Mount screenshots and videos folders as volumes [OK]

Common Mistakes:

• Not mounting screenshots/videos folders separately
• Using -p port mapping instead of volume mounts
• Assuming --save-artifacts flag exists