parallelize

Parallelizes the test suite.

Takes a workers argument that controls how many times the process is forked. For each process a new database will be created suffixed with the worker number.

test-database-0
test-database-1

If ENV["PARALLEL_WORKERS"] is set the workers argument will be ignored and the environment variable will be used instead. This is useful for CI environments, or other environments where you may need more workers than you do for local testing.

If the number of workers is set to 1 or fewer, the tests will not be parallelized.

If workers is set to :number_of_processors, the number of workers will be set to the actual core count on the machine you are on.

The default parallelization method is to fork processes. If you’d like to use threads instead you can pass with: :threads to the parallelize method. Note the threaded parallelization does not create multiple database and will not work with system tests at this time.

parallelize(workers: :number_of_processors, with: :threads)

The threaded parallelization uses minitest’s parallel executor directly. The processes parallelization uses a Ruby DRb server.

Because parallelization presents an overhead, it is only enabled when the number of tests to run is above the threshold param. The default value is 50, and it’s configurable via config.active_support.test_parallelization_threshold.