test: add MetricFactoryTest

inspectit-gepard-agent/build.gradle

@@ -108,6 +108,7 @@ dependencies {
     testCompileOnly("io.opentelemetry.javaagent:opentelemetry-javaagent-extension-api")
     testCompileOnly("io.opentelemetry:opentelemetry-sdk-extension-autoconfigure-spi")
     testCompileOnly("io.opentelemetry.javaagent:opentelemetry-javaagent-bootstrap")
+    testCompileOnly("io.opentelemetry:opentelemetry-exporter-logging")
 
     testImplementation("org.junit.jupiter:junit-jupiter-api:${versions.junit}")
     testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:${versions.junit}")

inspectit-gepard-agent/src/test/java/rocks/inspectit/gepard/agent/internal/metrics/MetricFactoryTest.java

@@ -0,0 +1,63 @@
+/* (C) 2024 */
+package rocks.inspectit.gepard.agent.internal.metrics;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.opentelemetry.api.GlobalOpenTelemetry;
+import io.opentelemetry.api.metrics.ObservableDoubleGauge;
+import io.opentelemetry.api.metrics.ObservableDoubleMeasurement;
+import io.opentelemetry.exporter.logging.LoggingMetricExporter;
+import io.opentelemetry.sdk.OpenTelemetrySdk;
+import io.opentelemetry.sdk.metrics.SdkMeterProvider;
+import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
+import java.time.Duration;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import rocks.inspectit.gepard.agent.internal.otel.OpenTelemetryAccessor;
+
+class MetricFactoryTest {
+
+  // Interval to read and export metrics
+  private static final Duration INTERVAL = Duration.ofMillis(500);
+
+  @BeforeAll
+  static void beforeAll() {
+    GlobalOpenTelemetry.resetForTest();
+
+    // Build our own OpenTelemetrySdk, so we don't use the NOOP implementations
+    SdkMeterProvider meterProvider =
+        SdkMeterProvider.builder()
+            .registerMetricReader(
+                PeriodicMetricReader.builder(LoggingMetricExporter.create())
+                    .setInterval(INTERVAL)
+                    .build())
+            .build();
+    OpenTelemetrySdk.builder().setMeterProvider(meterProvider).buildAndRegisterGlobal();
+    OpenTelemetryAccessor.setOpenTelemetry(GlobalOpenTelemetry.get());
+  }
+
+  @Test
+  void shouldRecordValueWithCallbackWhenCreatingGauge() throws InterruptedException {
+    AtomicBoolean valueRecorded = new AtomicBoolean(false);
+
+    Consumer<ObservableDoubleMeasurement> callback1 = (measurement) -> valueRecorded.set(true);
+    Consumer<ObservableDoubleMeasurement> callback2 =
+        (measurement) -> {
+          throw new RuntimeException("Test exception");
+        };
+
+    ObservableDoubleGauge gauge1 =
+        MetricFactory.createObservableDoubleGauge("test-gauge", callback1);
+    ObservableDoubleGauge gauge2 =
+        MetricFactory.createObservableDoubleGauge("fail-gauge", callback2);
+    // Wait for MetricReader
+    Thread.sleep(INTERVAL.toMillis() + 100);
+
+    assertTrue(valueRecorded.get());
+
+    gauge1.close();
+    gauge2.close();
+  }
+}