Docker execution in Cypress - Build an Automation Script

Run Cypress tests inside Docker container

Preconditions (3)

Step 1: Build the Docker image using the Dockerfile

Step 2: Run the Docker container from the built image

Step 3: Inside the container, execute Cypress tests

Step 4: Observe the test execution output in the container logs

✅ Expected Result: Cypress tests run successfully inside the Docker container and test results are visible in the container logs

Automation Requirements - Cypress

Assertions Needed:

Verify Cypress tests pass inside Docker container

Verify container exits with code 0 indicating success

Best Practices:

Use official Cypress Docker image as base

Mount project folder as volume for test code

Use explicit commands to run Cypress tests

Capture and assert exit code of container

Automated Solution

Cypress

const { execSync } = require('child_process');

describe('Docker execution of Cypress tests', () => {
  it('should build Docker image and run Cypress tests successfully', () => {
    // Build Docker image
    execSync('docker build -t cypress-test-image .', { stdio: 'inherit' });

    // Run Docker container and capture output
    const output = execSync('docker run --rm cypress-test-image', { encoding: 'utf-8' });

    // Check output contains test pass indication
    expect(output).to.include('All specs passed!');
  });
});

This Cypress test script uses Node.js execSync to run Docker commands synchronously.

First, it builds the Docker image named cypress-test-image using the Dockerfile in the current folder.

Then, it runs the container from that image and captures the output logs.

The test asserts that the output contains the text All specs passed! which Cypress prints when tests pass.

This confirms that Cypress tests ran successfully inside the Docker container.

Using execSync with stdio: 'inherit' streams Docker build logs to console for visibility.

Common Mistakes - 4 Pitfalls

Not using the official Cypress Docker image as base

{'mistake': 'Not mounting the project folder as a volume', 'why_bad': "Test code changes won't be reflected inside the container, causing stale tests to run.", 'correct_approach': 'Mount the project folder as a volume to ensure latest test code is used.'}

Ignoring container exit codes

Using asynchronous Docker commands without waiting

Bonus Challenge

Now add data-driven testing by running Cypress tests inside Docker with three different environment variables

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