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Context Caching

Once the TestContext framework loads an ApplicationContext (or WebApplicationContext) for a test, that context is cached and reused for all subsequent tests that declare the same unique context configuration within the same test suite. To understand how caching works, it is important to understand what is meant by “unique” and “test suite.”

An ApplicationContext can be uniquely identified by the combination of configuration parameters that is used to load it. Consequently, the unique combination of configuration parameters is used to generate a key under which the context is cached. The TestContext framework uses the following configuration parameters to build the context cache key:

  • locations (from @ContextConfiguration)

  • classes (from @ContextConfiguration)

  • contextInitializerClasses (from @ContextConfiguration)

  • contextCustomizers (from ContextCustomizerFactory) – this includes @DynamicPropertySource methods as well as various features from Spring Boot’s testing support such as @MockBean and @SpyBean.

  • contextLoader (from @ContextConfiguration)

  • parent (from @ContextHierarchy)

  • activeProfiles (from @ActiveProfiles)

  • propertySourceLocations (from @TestPropertySource)

  • propertySourceProperties (from @TestPropertySource)

  • resourceBasePath (from @WebAppConfiguration)

For example, if TestClassA specifies {"app-config.xml", "test-config.xml"} for the locations (or value) attribute of @ContextConfiguration, the TestContext framework loads the corresponding ApplicationContext and stores it in a static context cache under a key that is based solely on those locations. So, if TestClassB also defines {"app-config.xml", "test-config.xml"} for its locations (either explicitly or implicitly through inheritance) but does not define @WebAppConfiguration, a different ContextLoader, different active profiles, different context initializers, different test property sources, or a different parent context, then the same ApplicationContext is shared by both test classes. This means that the setup cost for loading an application context is incurred only once (per test suite), and subsequent test execution is much faster.

Test suites and forked processes

The Spring TestContext framework stores application contexts in a static cache. This means that the context is literally stored in a static variable. In other words, if tests run in separate processes, the static cache is cleared between each test execution, which effectively disables the caching mechanism.

To benefit from the caching mechanism, all tests must run within the same process or test suite. This can be achieved by executing all tests as a group within an IDE. Similarly, when executing tests with a build framework such as Ant, Maven, or Gradle, it is important to make sure that the build framework does not fork between tests. For example, if the forkMode for the Maven Surefire plug-in is set to always or pertest, the TestContext framework cannot cache application contexts between test classes, and the build process runs significantly more slowly as a result.

The size of the context cache is bounded with a default maximum size of 32. Whenever the maximum size is reached, a least recently used (LRU) eviction policy is used to evict and close stale contexts. You can configure the maximum size from the command line or a build script by setting a JVM system property named spring.test.context.cache.maxSize. As an alternative, you can set the same property via the SpringProperties mechanism.

Since having a large number of application contexts loaded within a given test suite can cause the suite to take an unnecessarily long time to run, it is often beneficial to know exactly how many contexts have been loaded and cached. To view the statistics for the underlying context cache, you can set the log level for the org.springframework.test.context.cache logging category to DEBUG.

In the unlikely case that a test corrupts the application context and requires reloading (for example, by modifying a bean definition or the state of an application object), you can annotate your test class or test method with @DirtiesContext (see the discussion of @DirtiesContext in Spring Testing Annotations ). This instructs Spring to remove the context from the cache and rebuild the application context before running the next test that requires the same application context. Note that support for the @DirtiesContext annotation is provided by the DirtiesContextBeforeModesTestExecutionListener and the DirtiesContextTestExecutionListener, which are enabled by default.

ApplicationContext lifecycle and console logging

When you need to debug a test executed with the Spring TestContext Framework, it can be useful to analyze the console output (that is, output to the SYSOUT and SYSERR streams). Some build tools and IDEs are able to associate console output with a given test; however, some console output cannot be easily associated with a given test.

With regard to console logging triggered by the Spring Framework itself or by components registered in the ApplicationContext, it is important to understand the lifecycle of an ApplicationContext that has been loaded by the Spring TestContext Framework within a test suite.

The ApplicationContext for a test is typically loaded when an instance of the test class is being prepared — for example, to perform dependency injection into @Autowired fields of the test instance. This means that any console logging triggered during the initialization of the ApplicationContext typically cannot be associated with an individual test method. However, if the context is closed immediately before the execution of a test method according to @DirtiesContext semantics, a new instance of the context will be loaded just prior to execution of the test method. In the latter scenario, an IDE or build tool may potentially associate console logging with the individual test method.

The ApplicationContext for a test can be closed via one of the following scenarios.

  • The context is closed according to @DirtiesContext semantics.

  • The context is closed because it has been automatically evicted from the cache according to the LRU eviction policy.

  • The context is closed via a JVM shutdown hook when the JVM for the test suite terminates.

If the context is closed according to @DirtiesContext semantics after a particular test method, an IDE or build tool may potentially associate console logging with the individual test method. If the context is closed according to @DirtiesContext semantics after a test class, any console logging triggered during the shutdown of the ApplicationContext cannot be associated with an individual test method. Similarly, any console logging triggered during the shutdown phase via a JVM shutdown hook cannot be associated with an individual test method.

When a Spring ApplicationContext is closed via a JVM shutdown hook, callbacks executed during the shutdown phase are executed on a thread named SpringContextShutdownHook. So, if you wish to disable console logging triggered when the ApplicationContext is closed via a JVM shutdown hook, you may be able to register a custom filter with your logging framework that allows you to ignore any logging initiated by that thread.