Reuse spring application context across junit test classes

We've a bunch of JUnit test cases (Integration tests) and they are logically grouped into different test classes.

We are able to load Spring application context once per test class and re-use it for all test cases in a JUnit test class as mentioned in http://static.springsource.org/spring/docs/current/spring-framework-reference/html/testing.html

However, we were just wondering if there is a way to load Spring application context only once for a bunch of JUnit test classes.

FWIW, we use Spring 3.0.5, JUnit 4.5 and use Maven to build the project.

Yes, this is perfectly possible. All you have to do is to use the same locations attribute in your test classes:

@ContextConfiguration(locations = "classpath:test-context.xml")

Spring caches application contexts by locations attribute so if the same locations appears for the second time, Spring uses the same context rather than creating a new one.

I wrote an article about this feature: Speeding up Spring integration tests. Also it is described in details in Spring documentation: 9.3.2.1 Context management and caching.

This has an interesting implication. Because Spring does not know when JUnit is done, it caches all context forever and closes them using JVM shutdown hook. This behavior (especially when you have a lot of test classes with different locations) might lead to excessive memory usage, memory leaks, etc. Another advantage of caching context.

To add to Tomasz Nurkiewicz's answer, as of Spring 3.2.2 @ContextHierarchy annotation can be used to have separate, associated multiple context structure. This is helpful when multiple test classes want to share (for example) in-memory database setups (datasource, EntityManagerFactory, tx manager etc).

For example:

@ContextHierarchy({
  @ContextConfiguration("/test-db-setup-context.xml"),
  @ContextConfiguration("FirstTest-context.xml")
})
@RunWith(SpringJUnit4ClassRunner.class)
public class FirstTest {
 ...
}

@ContextHierarchy({
  @ContextConfiguration("/test-db-setup-context.xml"),
  @ContextConfiguration("SecondTest-context.xml")
})
@RunWith(SpringJUnit4ClassRunner.class)
public class SecondTest {
 ...
}

By having this setup the context that uses "test-db-setup-context.xml" will only be created once, but beans inside it can be injected to individual unit test's context

More on the manual: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/testing.html#testcontext-ctx-management (search for "context hierarchy")

Basically spring is smart enough to configure this for you if you have the same application context configuration across the different test classes. For instance let's say you have two classes A and B as follows:

@ActiveProfiles("h2")
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class A {

    @MockBean
    private C c;
    //Autowired fields, test cases etc...
}

@ActiveProfiles("h2")
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class B {

    @MockBean
    private D d;
    //Autowired fields, test cases etc...
}

In this example class A mocks bean C, whereas class B mocks bean D. So, spring considers these as two different configurations and thus would load the application context once for class A and once for class B.

If instead, we'd want to have spring share the application context between these two classes, they would have to look something as follows:

@ActiveProfiles("h2")
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class A {

    @MockBean
    private C c;

    @MockBean
    private D d;
    //Autowired fields, test cases etc...
}

@ActiveProfiles("h2")
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class B {

    @MockBean
    private C c;

    @MockBean
    private D d;
    //Autowired fields, test cases etc...
}

If you wire up your classes like this, spring would load the application context only once either for class A or B depending on which class among the two is ran first in the test suite. This could be replicated across multiple test classes, only criteria is that you should not customize the test classes differently. Any customization that results in the test class to be different from the other(in the eyes of spring) would end up creating another application context by spring.

One remarkable point is that if we use @SpringBootTests but again use @MockBean in different test classes, Spring has no way to reuse its application context for all tests.

Solution is to move all @MockBean into an common abstract class and that fix the issue.

@SpringBootTests(webEnvironment = WebEnvironment.RANDOM_PORT, classes = Application.class)
public abstract class AbstractIT {

   @MockBean
   private ProductService productService;

   @MockBean
   private InvoiceService invoiceService;

}

Then the test classes can be seen as below

public class ProductControllerIT extends AbstractIT {
   // please don't use @MockBean here
   @Test
   public void searchProduct_ShouldSuccess() {
   }

}

public class InvoiceControllerIT extends AbstractIT {
   // please don't use @MockBean here
   @Test
   public void searchInvoice_ShouldSuccess() {
   }

}