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Parallel execution of tests

Module 5. Spring
Level 11 , Lesson 11
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Spring Framework 5.0 introduced basic support for running tests in parallel within the same JVM when using the Spring TestContext Framework. In general, this means that most test classes or test methods can be executed in parallel without any changes to the test code or configuration.

Refer to the documentation for your test system, build tool, or IDE for details on how to set up parallel execution of tests.

Remember that introducing parallelism into a test suite can result in unexpected side effects, unusual logic during program execution, and may cause tests to fail intermittently or randomly. Therefore, the Spring Team offers the following general guidelines regarding cases in which tests should not be run in parallel.

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Do not run tests in parallel if the tests:

  • Uses the @DirtiesContext annotation support in the Spring Framework.

  • Use Spring Boot's @MockBean or @SpyBean annotation support.

  • Use support for the @FixMethodOrder annotation in JUnit 4, or any test framework feature that is designed to ensure that test methods are executed in a specific order. Note, however, that this does not apply when entire test classes are executed in parallel.

  • Changing the state of shared services or systems such as the database, message broker, file system, and others. This applies to both embedded and external systems.

If a parallel test execution fails with an exception stating that the ApplicationContext for the current test is no longer active, this usually means that the ApplicationContext has been removed from the ContextCache in another thread.

This may be due to the use of the @DirtiesContext annotation or due to automatic eviction from ContextCache. If the culprit is the @DirtiesContext annotation, then you need to either find a way to avoid using @DirtiesContext or exclude such tests from parallel execution. If the ContextCache maximum size has been exceeded, you can increase the maximum cache size. For more details, see the description in the section on context caching.

Parallel execution of tests in the Spring TestContext Framework is only possible if the underlying TestContext implementation provides a copy constructor as described in the javadoc for TestContext. The DefaultTestContext used in Spring provides such a constructor. However, if you are using a third-party library that provides a custom TestContext implementation, you will need to ensure that it is suitable for running tests in parallel.
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