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Document methods of starting Testcontainer containers
Update the reference documentation to provide more details about the
three supported methods of starting Testcontainer containers.
See gh-44187
Signed-off-by: Vanio Begic <vanio.begic123@gmail.com>
Copy file name to clipboardExpand all lines: spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/testing/testcontainers.adoc
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@@ -5,13 +5,89 @@ The https://www.testcontainers.org/[Testcontainers] library provides a way to ma
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It integrates with JUnit, allowing you to write a test class that can start up a container before any of the tests run.
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Testcontainers is especially useful for writing integration tests that talk to a real backend service such as MySQL, MongoDB, Cassandra and others.
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In following sections we will describe some of the methods you can use to integrate Testcontainers with your tests.
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[[testing.testcontainers.via-junit-extension]]
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== Using via @Testcontainers JUnit5 extension
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The Testcontainers provides JUnit5 extensions, which can be used to manage containers in your tests.
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The extension is activated by applying the `@Testcontainers` annotation from Testcontainers to your test class.
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Testcontainers can be used in a Spring Boot test as follows:
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include-code::vanilla/MyIntegrationTests[]
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This will start up a docker container running Neo4j (if Docker is running locally) before any of the tests are run.
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This will start up a Docker container running Neo4j (if Docker is running locally) before any of the tests are run.
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In most cases, you will need to configure the application to connect to the service running in the container.
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In this case the lifecycle of the container instance is managed by Testcontainers, as described in official documentation.
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[[testing.testcontainers.via-spring-beans]]
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== Using via Spring managed beans
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The containers provided by Testcontainers can be managed by Spring Boot as beans.
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This method of managing contains can be used in combination with javadoc:org.springframework.boot.testcontainers.service.connection.ServiceConnection[format=annotation].
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To use Testcontainer contains as Spring beans we need to create a configuration class declaring the container as bean:
== Using via importing container declaration classes
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A common pattern with Testcontainers is to declare the Container instances as static fields in an interface.
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For example the following interface `MyInterface` declares two containers, one named `mongo` of type MongoDB and another named `neo` of type Neo4j:
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include-code::importcontainers/MyInterface[]
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When you have containers declared in this way, then you can have these containers managed by Spring Boot as beans.
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All that is needed to do that is adding javadoc:org.springframework.boot.testcontainers.context.ImportTestcontainers[format=annotation] to your configuration class as in:
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include-code::importcontainers/MyConfiguration[]
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TIP: Using interfaces for declaring contains helps with reuse.
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When containers are declared in an interface, this can be reused in your javadoc:org.springframework.context.annotation.Configuration[format=annotation] classes and in test classes.
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[[test.testcontainers.container-lifecycle]]
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== Lifecycle of managed containers
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If you have used the annotations and extensions provided by Testcontainers, then the lifecycle of container instances is managed by the Testcontainers.
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Please refer to the {url-testcontainres-java-doc}[Testcontainers official documentation] for the information about lifecycle of the containers, when managed by the Testcontainers.
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When the containers are managed by Spring as beans, then the lifecycle is clearly defined by Spring.
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The container beans are created and started before the beans of other types are created.
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This process ensures that any beans, which rely on functionality provided by the containers, can use those functionalities.
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The test containers can be started multiple times.
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Like any other beans the test containers are created and started once per application context managed by the TestContext Framework.
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For details about how TestContext framework manages the underlying application contexts and beans therein, please refer to the {url-spring-framework-docs}[official Spring documentation].
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The container beans are stopped after the destruction of beans of other types.
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This ensures that any beans depending on the functionalities provided by the containers are cleaned up first.
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TIP: When your application beans rely on functionality of containers, prefer configuring the containers as Spring beans.
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When containers are managed as Spring beans, then Spring framework ensures that upon start the container beans are started before any beans relying on them.
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On shutdown the application beans depending on container functionalities are cleaned up first, and only then are the containers shut down.
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NOTE: Having containers managed by Testcontainers instead of as Spring beans provides no guarantee of order in which beans and containers will shutdown.
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It can happen that containers are shutdown before the beans relying on container functionality are cleaned up.
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This can lead to exceptions being thrown by client beans due to loss of connection for example.
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The containers are stopped as part of the application shutdown process, managed by the TestContext framework.
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When the application context gets shutdown, the containers are shutdown as well.
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This usually happens after all tests using that specific cached application context have finished executing, but may happen earlier depending on the caching behavior configured in TestContext Framework.
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It is important to note that a single test container instance can be, and often is, retained across execution of tests from multiple test classes.
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