Run Tests in Parallel

Learn how to run your tests in parallel for faster build completion.

We automatically split your spec files, and run the tests on the specified browsers & OS automatically depending on the parallelization settings you’ve configured.

You can specify the number of parallels you want to use for running your tests in two ways:

  1. Using the CLI param
  2. Mentioning the parallels limit in the browserstack.json

Using the CLI

You can also use the --parallels option of the CLI while running your tests to specify the number of parallels you want to use to run your tests in parallel.

For example:

Command Line
browserstack-cypress run --parallels 5

Using browserstack.json

You can use parallels key in the run_settings option in the configuration file. You’ll need to mention the number of parallels you want to use to run your tests in parallel

For example:

  "run_settings": {
    "parallels": 5,

Parallelization strategy with an example

Let’s assume a scenario where you have 100 spec files, and want to run tests on the following 3 OS-browser combinations:

  • Chrome 80 on Windows 10
  • Edge 81 on OS X Mojave
  • Firefox 70 on OS X Catalina

If you specify to use 25 parallels, we will try to run the tests as follows depending on how many parallels are available to run your tests:

  • We will use 9 machines with Windows 10 & Chrome 80 to run 100 spec files.
  • We will use 8 machines each with the other two OS-browser combination to run the 100 spec files on those two OS-browser combinations.

If you specify to use 1 parallel, we will first run all 100 spec files on one machine with Chrome 80 on Windows 10, then do the same with the other two combinations. Obviously, this config will take much longer to finish running.

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