Remove mention of @TestComponent from the documentation as it is an implementation detail of @TestConfiguration

[michael-simons]

Hi,

hopefully I'm not doing anything wrong here. I assume that @TestComponent should be picked up when running tests with @SpringBootTest without further ado, but neither this

package com.example;

import org.springframework.boot.test.context.TestComponent;

@TestComponent
public class ToplevelTestComponent {
    
}

together with

package com.example;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class ToplevelTestComponentNotWorkingTest {
    @Autowired
    ToplevelTestComponent toplevelTestComponent;
    
    @Test
    public void f() {
    }
}

nor this (nested version)

package com.example;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.TestComponent;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class NestedTestComponentNotWorkingTest {
    @TestComponent
    static class NestedTestComponent{
    }
    
    @Autowired
    NestedTestComponent nestedTestComponent;
    
    @Test
    public void f() {
    }
}

works. Both fail with org.springframework.beans.factory.NoSuchBeanDefinitionException.
Sample project is attached:
InitializrSpringbootProject.zip
Tested with 1.4.0, 1.4.3 and 1.5.1.

Maybe it's a documentation issue, but I don't see my error…

[snicoll]

Javadoc:

@component that can be used when a bean is intended only for tests, and should be excluded from Spring Boot's component scanning.

Documentation:

To help prevent this, Spring Boot provides @TestComponent and @TestConfiguration annotations that can be used on classes in src/test/java to indicate that they should not be picked up by scanning.

What do you expect based on the doc?

[michael-simons]

Exactly the example above: Annotating a pojo in src/test/java with only @TestComponent with the result that it gets picked up during test, not that I have to use both @Component and @TestComponent.

[michael-simons]

If I have an @Component inside src/test/java, it get's picked up only during tests anyway, not during normal start. I cannot annotate any component inside src/main/java with @TestComponent having spring-boot-starter-test as test dependency.

[snicoll]

I am not following, the doc states that it will not be picked up by component scan. Why do you want it to be picked up all the sudden then? @TestConfiguration aren't picked up by component scan either ...

[snicoll]

Perhaps we could turn that one into a documentation enhancement. I am not excluding that @philwebb had something else in mind that I didn't get so it's certainly a good use of our time.

[michael-simons]

Sadly, you gave up when I just understood the purpose of @TestComponent.

I'd recommend you separate it a bit from @TestConfiguration in the docs and state that @TestComponent facilitate the creation of @TestConfiguration.

(TBH: I wonder if @TestComponent belongs into the reference at all or should only be part of JavaDoc)

Thanks, @snicoll for the good discussion. Got it now.

[snicoll]

The conversation on gitter was going in circles. If we've added that in the doc explicitly, I guess there's a reason I am missing anyway so we'll follow-up here for sure.