Do you use BitBucket Pipeline as your CI server? Are you struggling with slow E2E tests in Cypress? Did you know BitBucket Pipeline can run parallel steps? You can use it to distribute your browser tests across several parallel steps to execute end-to-end Cypress tests in a short amount of time.

How to run tests in parallel

Distributing tests across parallel steps to spread the workload and run tests faster might be more challenging than you think. The question is how to divide Cypress test files across the parallel jobs in order to ensure the work is distributed evenly? But... is distributing work evenly what you actually want?

To get the shortest CI build time you want to utilize the available CI resources to the fullest. You want to avoid wasting time. This means that you want to ensure the parallel steps will finish work at a similar time as this would mean there are no bottlenecks in CI machines utilization.

Many things are unknown and unpredictable. This can affect how long it will take to execute tests on BitBucket Pipeline. There are things like:

• boot time - time spent on loading your CI docker container
• loading npm/yarn dependencies from cache
• running Cypress tests
• tests can run against different browsers and this can affect how long the tests are executed
• sometimes tests can fail and their execution time is different
• other times you may have flaky tests randomly failing and you could use Test Retries in Cypress to automatically rerun failed test cases. This results in running a test file for longer.

All of the above contribute to the uncertainty around execution time. It's hard to know how best to divide test files across the parallel steps to ensure the steps complete work at a similar time. But there is a solution to that - a dynamic test suite split during runtime.

Queue Mode - a dynamic tests split

To distribute tests work across BitBucket Pipeline parallel steps you can use Knapsack Pro with a Queue Mode. You can use @knapsack-pro/cypress npm package that will generate a Queue with a list of test files on the Knapsack Pro API side and then all parallel steps can connect to the queue to consume test files and execute them. This way parallel steps ask for more tests only after they finish executing a set of tests previously fetched from the Knapsack Pro API. You can learn about the details of Queue Mode from the article.

BitBucket Pipeline YML config

Here is an example of a BitBucket Pipeline config in YML. As you can see, there are 3 parallel steps to run Cypress tests via Knapsack Pro. If you would like to run your tests on more parallel jobs you simply need to add more steps.

image: cypress/base:10
options:
  max-time: 30

# job definition for running E2E tests in parallel with KnapsackPro.com
e2e: &e2e
  name: Run E2E tests with @knapsack-pro/cypress
  caches:
    - node
    - cypress
  script:
    # run web application in the background
    - npm run start:ci &
    # env vars from https://support.atlassian.com/bitbucket-cloud/docs/variables-and-secrets/
    - export KNAPSACK_PRO_CI_NODE_BUILD_ID=$BITBUCKET_BUILD_NUMBER
    - export KNAPSACK_PRO_COMMIT_HASH=$BITBUCKET_COMMIT
    - export KNAPSACK_PRO_BRANCH=$BITBUCKET_BRANCH
    - export KNAPSACK_PRO_CI_NODE_TOTAL=$BITBUCKET_PARALLEL_STEP
    - export KNAPSACK_PRO_CI_NODE_INDEX=$BITBUCKET_PARALLEL_STEP_COUNT
    # https://github.com/KnapsackPro/knapsack-pro-cypress#configuration-steps
    - export KNAPSACK_PRO_FIXED_QUEUE_SPLIT=true
    - $(npm bin)/knapsack-pro-cypress
  artifacts:
    # store any generated images and videos as artifacts
    - cypress/screenshots/**
    - cypress/videos/**

pipelines:
  default:
  - step:
      name: Install dependencies
      caches:
        - npm
        - cypress
        - node
      script:
        - npm ci
  - parallel:
    # run N steps in parallel
    - step:
        <<: *e2e
    - step:
        <<: *e2e
    - step:
        <<: *e2e

definitions:
  caches:
    npm: $HOME/.npm
    cypress: $HOME/.cache/Cypress

If you are looking for an example with a custom docker container for a parallel step please see this one.

Please remember to add your API token in the KNAPSACK_PRO_TEST_SUITE_TOKEN_CYPRESS environment variable as a secure variable.

Summary

BitBucket Pipeline is a CI server that allows running scripts in parallel. You can use parallel steps to distribute your Cypress tests with Knapsack Pro to save time and run CI build as fast as possible.