Add smoke test for Prometheus

See gh-40904

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-prometheus/build.gradle

@@ -0,0 +1,15 @@
+plugins {
+	id "java"
+	id "org.springframework.boot.conventions"
+}
+
+description = "Spring Boot Prometheus smoke test"
+
+dependencies {
+	implementation(project(":spring-boot-project:spring-boot-starters:spring-boot-starter-web"))
+	implementation(project(":spring-boot-project:spring-boot-starters:spring-boot-starter-actuator"))
+	implementation('io.micrometer:micrometer-tracing-bridge-brave')
+	runtimeOnly('io.micrometer:micrometer-registry-prometheus')
+
+	testImplementation(project(":spring-boot-project:spring-boot-starters:spring-boot-starter-test"))
+}

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-prometheus/src/main/java/smoketest/prometheus/SamplePrometheusApplication.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2012-2024 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 smoketest.prometheus;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class SamplePrometheusApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(SamplePrometheusApplication.class, args);
+	}
+
+}

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-prometheus/src/main/resources/application.properties

@@ -0,0 +1,2 @@
+management.endpoints.web.exposure.include=*
+management.tracing.sampling.probability=1.0

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-prometheus/src/test/java/smoketest/prometheus/SamplePrometheusApplicationTests.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2012-2024 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 smoketest.prometheus;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.actuate.observability.AutoConfigureObservability;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link SamplePrometheusApplication}.
+ *
+ * @author Moritz Halbritter
+ */
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
+@AutoConfigureObservability
+class SamplePrometheusApplicationTests {
+
+	@Autowired
+	private TestRestTemplate restTemplate;
+
+	@Test
+	void shouldExportExemplars() {
+		for (int i = 0; i < 10; i++) {
+			ResponseEntity<String> response = this.restTemplate.getForEntity("/actuator", String.class);
+			assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
+		}
+		HttpHeaders headers = new HttpHeaders();
+		headers.add(HttpHeaders.ACCEPT, "application/openmetrics-text; version=1.0.0; charset=utf-8");
+		ResponseEntity<String> metrics = this.restTemplate.exchange("/actuator/prometheus", HttpMethod.GET,
+				new HttpEntity<>(headers), String.class);
+		assertThat(metrics.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(metrics.getBody()).containsSubsequence("http_client_requests_seconds_count", "span_id", "trace_id");
+	}
+
+}