Improve @PropertyMapping annotations can only be used on test classes message

[wilkinsona]

This is a follow-on from #5882.

In trying to produce the idiomatic 1.4 equivalent of @dsyer's slightly unusual test I discovered that @PropertyMapping prevents a test class from also being annotation with @Component. For example, this will fall in a heap:

@RunWith(SpringRunner.class)
@WebMvcTest
@RestController
public class WebMvcTests {

    private static Log logger = LogFactory.getLog(WebMvcTests.class);

    @Autowired
    private MockMvc mockMvc;

    private static Object span;

    @RequestMapping("/ping")
    public String ping() {
        logger.info("ping");
        WebMvcTests.span = new Object();
        return "ping";
    }

    @RequestMapping("/future")
    public CompletableFuture<String> future() {
        logger.info("future");
        return CompletableFuture.completedFuture("ping");
    }

    @Test
    public void getCallsEndpoint() throws Exception {
        this.mockMvc.perform(get("/ping")).andDo(print());
        assertThat(WebMvcTests.span, is(notNullValue()));
    }

    @Test
    public void futureCreatesAsync() throws Exception {
        this.mockMvc.perform(get("/future")).andExpect(request().asyncStarted());
    }

}

The failure is:

java.lang.IllegalStateException: @PropertyMapping annotations can only be used on test classes
    at org.springframework.util.Assert.state(Assert.java:392)
    at org.springframework.boot.test.autoconfigure.properties.PropertyMappingContextCustomizer$PropertyMappingCheckBeanPostProcessor.postProcessBeforeInitialization(PropertyMappingContextCustomizer.java:80)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:408)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1570)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:399)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:119)
    at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:83)
    at org.springframework.boot.test.autoconfigure.AutoConfigureReportTestExecutionListener.prepareTestInstance(AutoConfigureReportTestExecutionListener.java:46)
    at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:230)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:228)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:287)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:289)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:247)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

The nearest equivalent in 1.4 that works is:

@RunWith(SpringRunner.class)
@WebMvcTest
public class WebMvcTests {

    private static Log logger = LogFactory.getLog(WebMvcTests.class);

    @Autowired
    private MockMvc mockMvc;

    private static Object span;

    @Test
    public void getCallsEndpoint() throws Exception {
        this.mockMvc.perform(get("/ping")).andDo(print());
        assertThat(WebMvcTests.span, is(notNullValue()));
    }

    @Test
    public void futureCreatesAsync() throws Exception {
        this.mockMvc.perform(get("/future")).andExpect(request().asyncStarted());
    }

    @TestConfiguration
    @RestController
    static class Foo {

        @RequestMapping("/ping")
        public String ping() {
            logger.info("ping");
            WebMvcTests.span = new Object();
            return "ping";
        }

        @RequestMapping("/future")
        public CompletableFuture<String> future() {
            logger.info("future");
            return CompletableFuture.completedFuture("ping");
        }

    }

}

[philwebb]

I think making the test itself a component is probably bad practice but we should certainly enhance the error message.

[philwebb]

A bit more digging. With the original test, two instances of WebMvcTests are created. The first is by JUnit and the second is by Spring. I think this is quite likely to cause other problems so we are best to still throw some kind of exception.