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[JUnit Platform] Update parallel execution documentation #2609

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[JUnit Platform] Update parallel execution documentation #2609

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28 changes: 23 additions & 5 deletions cucumber-junit-platform-engine/README.md
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Expand Up @@ -185,14 +185,32 @@ in parallel is available as an opt-in feature. To enable parallel execution, set
the `cucumber.execution.parallel.enabled` configuration parameter to `true`,
e.g. in `junit-platform.properties`.

Cucumber supports JUnit's `ParallelExecutionConfigurationStrategy`; see the
configuration options below.
To control properties such as the desired parallelism and maximum parallelism,
Cucumber supports JUnit 5s `ParallelExecutionConfigurationStrategy`. Cucumber
provides two implementations: `dynamic` and `fixed` that can be set through
`cucumber.execution.parallel.config.strategy`. You may also implement a `custom`
strategy.

* `dynamic`: Computes the desired parallelism as `<available cores>` *
`cucumber.execution.parallel.config.dynamic.factor`.

* `fixed`: Set the desired parallelism to `cucumber.execution.parallel.config.fixed.parallelism`.

* `custom`: Specify a custom `ParallelExecutionConfigurationStrategy`
implementation through `cucumber.execution.parallel.config.custom.class`.

If no strategy is specified Cucumber will use the `dynamic` strategy with a
factor of `1`.

Note: Cucumber does not guarantee that the number of concurrently executing
tests will not exceed the configured parallelism. The underlying `ForkJoinPool`
used to execute scenarios may spawn additional threads. To obtain such
guarantees us a custom parallel configuration strategy.

### Exclusive Resources ###

The JUnit Platform supports parallel execution. To avoid flaky tests when
multiple scenarios manipulate the same resource, tests can be
[synchronized][junit5-user-guide-synchronization] on that resource.
To avoid flaky tests when multiple scenarios manipulate the same resource, tests
can be [synchronized][junit5-user-guide-synchronization] on that resource.

[junit5-user-guide-synchronization]: https://junit.org/junit5/docs/current/user-guide/#writing-tests-parallel-execution-synchronization

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