Implement test resources property provider factory

[melix]

This commit introduces a new annotation, @TestResourceProperties, which can be applied on a test in order to tell that the test needs to resolve one or more test resource properties before the application context is available.

For example, with:

@MicronautTest
@TestResourcesProperties(
    value = "redis.url"
)
class SomeTest { ... }

Then the value of the redis.url property will automatically be fetched from the test resources service and made available as if it had been done in a TestPropertyProvider. The difference is that this without this annotation, it was required to call the test resources client directly in the provider, which was error prone. In particular, the properties argument of the resolve call are not easy to figure out.

This annotation is therefore a convention to avoid having to call the client directly. However, in some cases it might be necessary to read a property in order to compute a different one which needs to be available in the test.

This can be done by adding a providers argument to the annotation:

@TestResourcesProperties(
    value = "rabbitmq.uri",
    providers = RabbitTest.RabbitMQProvider.class
)
class RabbitTest {
  // ...
      @ReflectiveAccess
      public static class RabbitMQProvider implements TestResourcesPropertyProvider {
          @Override
          public Map<String, String> provide(Map<String, Object> testProperties) {
              String uri = (String) testProperties.get("rabbitmq.uri");
              return Map.of(
                  "rabbitmq.servers.product-cluster.port", String.valueOf(URI.create(uri).getPort())
              );
          }
      }
}

The TestResourcesPropertyProvider type has access to all properties which are already resolved at the moment it is called, which includes the properties asked in @TestResourcesProperties.

This should make the implementation of micronaut-projects/micronaut-nats#321 easier.

[graemerocher]

Concept looks fine needs more javadoc and some reference documentation explaining how to use it

[graemerocher]

Some reference docs would be nice

[melix]

Some reference docs would be nice

Yes, but I'd like to finish the improvements first (there should be another PR on this topic, with scope management).