Parallel execution in Cypress

Introduction

Parallel execution helps run multiple tests at the same time. This makes testing faster and saves time.

You have many tests and want to finish them quickly.

You want to test your app on different browsers or devices at once.

You want to reduce waiting time during continuous integration.

You want to use multiple machines or servers to run tests together.

You want faster feedback after code changes.

Syntax

Cypress

cypress run --parallel --record --key <record-key>

Use --parallel flag to enable parallel test runs.

--record and --key are needed to connect with Cypress Dashboard for parallel support.

Examples

Runs tests in parallel using the Cypress Dashboard with the project key abc123.

Cypress

cypress run --parallel --record --key abc123

Runs tests recorded to the Dashboard but without parallel execution.

Cypress

cypress run --record --key abc123

Runs tests sequentially without recording or parallel execution.

Cypress

cypress run

Sample Program

This config sets up Cypress to run all tests in the cypress/e2e folder. Running the command with --parallel will split tests across available machines or containers to run at the same time.

Cypress

// cypress.config.js
module.exports = {
  e2e: {
    setupNodeEvents(on, config) {
      // no special setup needed for parallel
    },
    specPattern: 'cypress/e2e/**/*.cy.js'
  }
}

// Run command in terminal:
cypress run --parallel --record --key abc123

Important Notes

You must use the Cypress Dashboard service to enable parallel execution.

Tests are split automatically based on spec files and available machines.

Make sure your tests are independent to avoid conflicts when running in parallel.

Summary

Parallel execution runs tests at the same time to save time.

Use cypress run --parallel --record --key <key> to enable it.

Requires Cypress Dashboard and independent tests for best results.

Practice

1. What is the main benefit of running tests in parallel in Cypress?

easy

A. It reduces the total test execution time by running tests simultaneously.

B. It makes tests run one after another to avoid conflicts.

C. It automatically fixes failing tests during execution.

D. It disables tests that are not needed for the current run.

Solution

1. Step 1: Understand parallel execution purpose

   Parallel execution means running multiple tests at the same time instead of one by one.

2. Step 2: Identify the benefit

   Running tests simultaneously saves time by reducing total test duration.

3. Final Answer:

   It reduces the total test execution time by running tests simultaneously. -> Option A

4. Quick Check:

   Parallel execution = faster test runs [OK]

Hint: Parallel means tests run together, saving time [OK]

Common Mistakes:

• Thinking tests run sequentially in parallel mode
• Assuming parallel fixes test failures automatically
• Believing parallel disables some tests

2. Which command correctly enables parallel test execution with recording in Cypress?

easy

A. cypress run --parallel --record --key <key>

B. cypress open --parallel --record --key <key>

C. cypress run --record --key <key>

D. cypress run --key <key> --parallel

Solution

1. Step 1: Recall correct Cypress CLI syntax

   The correct command to run tests in parallel with recording is cypress run --parallel --record --key <key>.

2. Step 2: Verify required flags and command

   The command must use cypress run (not open), include --parallel for parallelization, and --record --key <key> for recording.

3. Final Answer:

   cypress run --parallel --record --key <key> -> Option A

4. Quick Check:

   Correct CLI command = cypress run --parallel --record --key <key> [OK]

Hint: cypress run + --parallel + --record --key [OK]

Common Mistakes:

• Using 'cypress open' instead of 'cypress run'
• Omitting the --record flag
• Omitting the --parallel flag

3. Given the following Cypress command run in parallel mode:

cypress run --parallel --record --key abc123

What is the expected behavior during test execution?

medium

A. Tests run one by one and results are not recorded.

B. Tests run simultaneously across multiple machines and results are recorded in the Dashboard.

C. Tests run only on a single machine without recording.

D. Tests run in parallel but results are saved locally only.

Solution

1. Step 1: Analyze the command flags

   The command uses --parallel to run tests simultaneously and --record with a --key to save results to Cypress Dashboard.

2. Step 2: Understand the effect on test execution

   Tests will run on multiple machines or processes at the same time, and results will be uploaded to the Dashboard for viewing.

3. Final Answer:

   Tests run simultaneously across multiple machines and results are recorded in the Dashboard. -> Option B

4. Quick Check:

   Parallel + record = simultaneous runs + Dashboard [OK]

Hint: Parallel + record means multiple machines and Dashboard [OK]

Common Mistakes:

• Assuming tests run sequentially despite --parallel
• Thinking results are saved only locally
• Ignoring the effect of --record and --key

4. You tried running Cypress tests in parallel but noticed tests are not splitting across machines. What is the most likely cause?

medium

A. Tests are not independent and share state, preventing parallel splitting.

B. You forgot to install Cypress Dashboard locally.

C. The command used was cypress open --parallel instead of cypress run --parallel.

D. Parallel execution requires tests to be written in JavaScript only.

Solution

1. Step 1: Understand requirements for parallel splitting

   Tests must be independent (no shared state) to split correctly across machines in parallel execution.

2. Step 2: Identify the cause of no splitting

   If tests share state or depend on each other, Cypress cannot split them properly, causing all tests to run on one machine.

3. Final Answer:

   The command used was cypress open --parallel instead of cypress run --parallel. -> Option C

4. Quick Check:

   Use 'cypress run' for parallel splitting [OK]

Hint: Tests must be independent to split in parallel [OK]

Common Mistakes:

• Confusing 'cypress open' with 'cypress run' for parallel
• Thinking Dashboard installation affects splitting
• Believing language type restricts parallel execution

5. You want to optimize your Cypress test suite using parallel execution but notice flaky failures when tests run simultaneously. What is the best approach to fix this?

hard

A. Run tests sequentially instead of parallel to avoid failures.

B. Disable recording to speed up test runs and reduce flakiness.

C. Increase the number of parallel machines without changing tests.

D. Refactor tests to be fully independent and avoid shared state or global data.

Solution

1. Step 1: Identify cause of flaky failures in parallel runs

   Flaky failures often happen because tests share state or interfere with each other when run simultaneously.

2. Step 2: Choose best fix for flaky parallel tests

   Refactoring tests to be independent and avoid shared global data ensures stable parallel execution.

3. Final Answer:

   Refactor tests to be fully independent and avoid shared state or global data. -> Option D

4. Quick Check:

   Independent tests fix flaky parallel runs [OK]

Hint: Make tests independent to fix flaky parallel runs [OK]

Common Mistakes:

• Just increasing machines without fixing tests
• Disabling recording does not fix flakiness
• Switching to sequential loses parallel benefits