Skip to main content
Version: 19.x

Parallel Test Execution

Parallel Test Execution​

Detox can leverage multi worker support of JS test runners (Jest, AVA, etc.).

By default detox test will run the test runner with one worker (it will pass --maxWorkers=1 to Jest CLI, Mocha is unaffected). Worker count can be controlled by adding --workers n to detox test, read more in detox-cli section.

Device Creation​

While running with multiple workers, Detox might not have an available simulator for every worker. If no simulator is available for that worker, the worker will create one with the name {name}-Detox.

Lock File​

Simulators/emulators run on a different process, outside of node, and require some sort of lock mechanism to make sure only one process controls a simulator in a given time. Therefore, Detox 7.4.0 introduced device.registry.state.lock, a lock file controlled by Detox, that registers all in-use simulators.

Note: Each worker is responsible for removing the device ID from the list in device.registry.state.lock. Exiting a test runner abruptly (using Ctrl+C / ⌘+C) will not give the worker a chance to unregister the device from the lock file, resulting in an inconsistent state, which can result in creation of unnecessary new simulators.

  • detox-cli makes sure device.registry.state.lock is cleaned whenever it executes.

  • If you use Detox without detox-cli make sure you delete or reset the lock file before running tests.

    echo "[]" > ~/Library/Detox/device.registry.state.lock

The lock file location is determined by the OS, and defined here.

  • MacOS: ~/Library/Detox/device.registry.state.lock
  • Linux: ~/.local/share/Detox/device.registry.state.lock
  • Windows: %LOCALAPPDATA%/data/Detox/device.registry.state.lock or %USERPROFILE%/Application Data/Detox/device.registry.state.lock

Persisting the Lock File​

By default, once all workers finish their test runs, Detox will delete the lock file. Under certain conditions, you may want to persist the lock file. Use the --keepLockFile flag to disable automatic deletion.