Auto-configure observatibility beans in sliced tests

If @AutoConfigureObservability is applied to a sliced test, it
auto-configures:

- An in-memory MeterRegistry
- A no-op Tracer
- An ObservationRegistry

Closes gh-38568

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/testing.adoc

@@ -255,13 +255,21 @@ If such test needs access to an `MBeanServer`, consider marking it dirty as well
 include::code:MyJmxTests[]
 
 
+[[features.testing.spring-boot-applications.observations]]
+==== Using Observations
+If you annotate <<features#features.testing.spring-boot-applications.autoconfigured-tests, a sliced test>> with `@AutoConfigureObservability`, it auto-configures an `ObservationRegistry`.
+
+
 
 [[features.testing.spring-boot-applications.metrics]]
 ==== Using Metrics
 Regardless of your classpath, meter registries, except the in-memory backed, are not auto-configured when using `@SpringBootTest`.
 
 If you need to export metrics to a different backend as part of an integration test, annotate it with `@AutoConfigureObservability`.
 
+If you annotate <<features#features.testing.spring-boot-applications.autoconfigured-tests, a sliced test>> with `@AutoConfigureObservability`, it auto-configures an in-memory `MeterRegistry`.
+Data exporting in sliced tests is not supported with the `@AutoConfigureObservability` annotation.
+
 
 
 [[features.testing.spring-boot-applications.tracing]]
@@ -272,6 +280,9 @@ If you need those components as part of an integration test, annotate the test w
 
 If you have created your own reporting components (e.g. a custom `SpanExporter` or `SpanHandler`) and you don't want them to be active in tests, you can use the `@ConditionalOnEnabledTracing` annotation to disable them.
 
+If you annotate <<features#features.testing.spring-boot-applications.autoconfigured-tests, a sliced test>> with `@AutoConfigureObservability`, it auto-configures a no-op `Tracer`.
+Data exporting in sliced tests is not supported with the `@AutoConfigureObservability` annotation.
+
 
 
 [[features.testing.spring-boot-applications.mocking-beans]]

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/actuate/observability/AutoConfigureObservability.java

@@ -23,9 +23,15 @@
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
+import org.springframework.boot.autoconfigure.ImportAutoConfiguration;
+
 /**
  * Annotation that can be applied to a test class to enable auto-configuration for
  * observability.
+ * <p>
+ * If this annotation is applied to a sliced test, an in-memory {@code MeterRegistry}, a
+ * no-op {@code Tracer} and an {@code ObservationRegistry} is added to the application
+ * context.
  *
  * @author Moritz Halbritter
  * @since 3.0.0
@@ -34,17 +40,18 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Inherited
+@ImportAutoConfiguration
 public @interface AutoConfigureObservability {
 
 	/**
-	 * Whether metrics should be enabled in the test.
-	 * @return whether metrics should be enabled in the test
+	 * Whether metrics should be reported to external systems in the test.
+	 * @return whether metrics should be reported to external systems in the test
 	 */
 	boolean metrics() default true;
 
 	/**
-	 * Whether tracing should be enabled in the test.
-	 * @return whether tracing should be enabled in the test
+	 * Whether traces should be reported to external systems in the test.
+	 * @return whether traces should be reported to external systems in the test
 	 */
 	boolean tracing() default true;
 

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring/org.springframework.boot.test.autoconfigure.actuate.observability.AutoConfigureObservability.imports

@@ -0,0 +1,13 @@
+# AutoConfigureObservability auto-configuration imports
+
+# Observation
+org.springframework.boot.actuate.autoconfigure.observation.ObservationAutoConfiguration
+
+# Metrics
+org.springframework.boot.actuate.autoconfigure.metrics.CompositeMeterRegistryAutoConfiguration
+org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration
+org.springframework.boot.actuate.autoconfigure.metrics.export.simple.SimpleMetricsExportAutoConfiguration
+
+# Tracing
+org.springframework.boot.actuate.autoconfigure.tracing.NoopTracerAutoConfiguration
+org.springframework.boot.actuate.autoconfigure.tracing.MicrometerTracingAutoConfiguration

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/actuate/observability/AutoConfigureObservabilitySlicedIntegrationTests.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2012-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.autoconfigure.actuate.observability;
+
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
+import io.micrometer.observation.ObservationRegistry;
+import io.micrometer.tracing.Tracer;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
+import org.springframework.context.ApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link AutoConfigureObservability} when used on a sliced test.
+ *
+ * @author Moritz Halbritter
+ */
+@WebMvcTest
+@AutoConfigureObservability
+class AutoConfigureObservabilitySlicedIntegrationTests {
+
+	@Autowired
+	private ApplicationContext context;
+
+	@Test
+	void shouldHaveTracer() {
+		assertThat(this.context.getBean(Tracer.class)).isEqualTo(Tracer.NOOP);
+	}
+
+	@Test
+	void shouldHaveMeterRegistry() {
+		assertThat(this.context.getBean(MeterRegistry.class)).isInstanceOf(SimpleMeterRegistry.class);
+	}
+
+	@Test
+	void shouldHaveObservationRegistry() {
+		assertThat(this.context.getBean(ObservationRegistry.class)).isNotNull();
+	}
+
+}