Add YamlPropertySourceFactory that can be used for loading YAML files through the @TestPropertySource annotation

[nosan]

I have prepared two potential solutions for this #33434 enhancement.

The first approach offers a simple and intuitive way to use it:

@SpringJUnitConfig
@TestPropertySource(locations = "classpath:test.yaml", factory = YamlPropertySourceFactory.class)
class SomeTest {

}

YamlPropertySourceFactory loads all properties from the specified YAML file using YamlPropertySourceLoader and returns a CompositePropertySource containing the loaded properties.

As a potential improvement, a dedicated annotation like @TestYamlPropertySource could be introduced to simplify the loading of YAML files in tests.

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@TestPropertySource(factory = YamlPropertySourceFactory.class)
@Repeatable(TestYamlPropertySources.class)
public @interface TestYamlPropertySource {

	@AliasFor(attribute = "value", annotation = TestPropertySource.class)
	String[] value() default {};

	@AliasFor(attribute = "locations", annotation = TestPropertySource.class)
	String[] locations() default {};

	@AliasFor(attribute = "inheritLocations", annotation = TestPropertySource.class)
	boolean inheritLocations() default true;

	@AliasFor(attribute = "properties", annotation = TestPropertySource.class)
	String[] properties() default {};

	@AliasFor(attribute = "inheritProperties", annotation = TestPropertySource.class)
	boolean inheritProperties() default true;

}

With a dedicated annotation, the following syntax could be supported:

@SpringJUnitConfig
@TestYamlPropertySource({ "classpath:test.yaml", "classpath:test1.yaml" })
@TestYamlPropertySource(locations = "classpath:test2.yaml", properties = "key:value")
class TestYamlPropertySourceIntegrationTests {

}

---

An alternative approach is to customize PropertySourceDescriptor in SpringBootTestContextBootstrapper by using the PropertySourceLoaderPropertySourceFactory, which leverages the existing PropertySourceLoader. With that approach, the following syntax would be possible:

@SpringBootTest
@TestPropertySource(locations = "classpath:test.yaml")
class SomeTest {
	
}

But it has several disadvantages:

• It works only with the @SpringBootTest annotation. For @SpringJUnitConfig, the factory needs to be explicitly used.

• It does not support EncodedResource for .properties files because PropertySourceLoader only works with Resource objects. As a result, if someone is using @TestPropertySource with the encoding attribute, these changes could potentially impact them.

• Not obvious.

The first approach is much better and straightforward, and people would not have any problem using it.

[nosan]

The third option
is similar to the first approach, but instead of supporting only .yaml files, it also
supports multi-document .properties.

@SpringJUnitConfig
@TestPropertySource(locations = { "classpath:test.yaml", "classpath:test1.yaml", "classpath:test.properties" },
		factory = PropertySourceLoaderPropertySourceFactory.class)
class PropertySourceLoaderPropertySourceFactoryIntegrationTests {

}

[philwebb]

I like YamlPropertySourceFactory since it's quite obvious what it does. Once thing that makes me pause is that we don't/can't support spring.config.activate.on-profile for multi-document files. We also can't support spring.config.import. I'm not sure if this is really a problem, but folks using the annotation will need to understand the restrictions.

[nosan]

Once thing that makes me pause is that we don't/can't support spring.config.activate.on-profile for multi-document files.

I was trying to add this support, but to be honest, I have not found a way.

I'm not sure if this is really a problem

I think most people will use a dedicated YAML file to configure their test context, and I doubt anyone will try to use the spring.config.activate.on-profile feature

but folks using the annotation will need to understand the restrictions.

I completely agree, and it would be beneficial to include this information in the Javadoc and documentation.

[philwebb]

Perhaps we should make it a hard requirement that only a single document is in the YAML and that no profile restrictions or imports are specified. We'll discuss this on a team call when can.

[philwebb]

I'm wondering if basic YAML support should be something that's added to Spring Framework. Perhaps with some hook point so that we can warn if users accidentally point at YAML files that won't work. What do you think @sbrannen?