chore: add showcase integration tests for OpenTelemetry parent context tracing (#14535)

Showcase end-to-end integration tests verifying parent trace context
linking for gRPC, HTTP/JSON, and retry attempt spans.

b/564460690

Author: jinseopkim0

java-showcase/gapic-showcase/src/test/java/com/google/showcase/v1beta1/it/ITOtelTracing.java

@@ -68,7 +68,10 @@
 import io.grpc.MethodDescriptor;
 import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.api.trace.SpanKind;
+import io.opentelemetry.api.trace.Tracer;
+import io.opentelemetry.context.Scope;
 import io.opentelemetry.sdk.OpenTelemetrySdk;
 import io.opentelemetry.sdk.testing.exporter.InMemorySpanExporter;
 import io.opentelemetry.sdk.trace.SdkTracerProvider;
@@ -129,6 +132,7 @@ class ITOtelTracing {
 
   private InMemorySpanExporter spanExporter;
   private OpenTelemetrySdk openTelemetrySdk;
+  private Tracer tracer;
 
   @BeforeEach
   void setup() {
@@ -141,6 +145,7 @@ void setup() {
 
     openTelemetrySdk =
         OpenTelemetrySdk.builder().setTracerProvider(tracerProvider).buildAndRegisterGlobal();
+    tracer = openTelemetrySdk.getTracer("it-otel-tracing-test");
   }
 
   @AfterEach
@@ -456,6 +461,69 @@ void testTracing_retry_grpc() throws Exception {
     assertThat(resendCounts).containsExactlyElementsIn(expectedCounts).inOrder();
   }
 
+  /**
+   * Verifies that when an RPC is invoked within an active OpenTelemetry trace context, all attempt
+   * spans (including the initial call and retries scheduled on background threads) properly link to
+   * the parent span context using gRPC transport.
+   */
+  @Test
+  void testTracing_retry_grpc_linkedToParentContext() throws Exception {
+    final int attempts = 5;
+    final StatusCode.Code statusCode = StatusCode.Code.UNAVAILABLE;
+    RetrySettings retrySettings =
+        RetrySettings.newBuilder()
+            .setTotalTimeout(org.threeten.bp.Duration.ofMillis(5000L))
+            .setMaxAttempts(attempts)
+            .build();
+
+    OpenTelemetryTracingFactory tracingFactory = new OpenTelemetryTracingFactory(openTelemetrySdk);
+
+    EchoSettings grpcEchoSettings = createEchoSettings(false);
+    EchoStubSettings.Builder grpcEchoSettingsBuilder =
+        (EchoStubSettings.Builder) grpcEchoSettings.getStubSettings().toBuilder();
+    grpcEchoSettingsBuilder
+        .echoSettings()
+        .setRetrySettings(retrySettings)
+        .setRetryableCodes(statusCode);
+    grpcEchoSettingsBuilder.setTracerFactory(tracingFactory);
+    EchoStub stub = new ExtendedEchoStubSettings(grpcEchoSettingsBuilder).createStub();
+    EchoClient grpcClient = EchoClient.create(stub);
+
+    EchoRequest echoRequest =
+        EchoRequest.newBuilder()
+            .setError(Status.newBuilder().setCode(statusCode.ordinal()).build())
+            .build();
+
+    Span parentSpan = tracer.spanBuilder("application-parent-operation").startSpan();
+    try (Scope scope = parentSpan.makeCurrent()) {
+      assertThrows(UnavailableException.class, () -> grpcClient.echo(echoRequest));
+    } finally {
+      parentSpan.end();
+    }
+
+    List<SpanData> spans = spanExporter.getFinishedSpanItems();
+    assertThat(spans).hasSize(attempts + 1);
+
+    SpanData rootSpan =
+        spans.stream()
+            .filter(span -> span.getName().equals("application-parent-operation"))
+            .findFirst()
+            .orElseThrow(() -> new AssertionError("Parent span not found"));
+
+    List<SpanData> attemptSpans =
+        spans.stream()
+            .filter(span -> span.getName().equals(SPAN_NAME_ECHO_GRPC))
+            .collect(java.util.stream.Collectors.toList());
+    assertThat(attemptSpans).hasSize(attempts);
+
+    for (SpanData attemptSpan : attemptSpans) {
+      assertThat(attemptSpan.getKind()).isEqualTo(SpanKind.CLIENT);
+      assertThat(attemptSpan.getParentSpanId()).isEqualTo(rootSpan.getSpanContext().getSpanId());
+      assertThat(attemptSpan.getSpanContext().getTraceId())
+          .isEqualTo(rootSpan.getSpanContext().getTraceId());
+    }
+  }
+
   @Test
   void testTracing_retry_httpjson() throws Exception {
     final int attempts = 5;
@@ -534,6 +602,69 @@ void testTracing_retry_httpjson() throws Exception {
     assertThat(resendCounts).containsExactlyElementsIn(expectedCounts).inOrder();
   }
 
+  /**
+   * Verifies that when an RPC is invoked within an active OpenTelemetry trace context, all attempt
+   * spans (including the initial call and retries scheduled on background threads) properly link to
+   * the parent span context using HTTP/JSON transport.
+   */
+  @Test
+  void testTracing_retry_httpjson_linkedToParentContext() throws Exception {
+    final int attempts = 5;
+    final StatusCode.Code statusCode = StatusCode.Code.INVALID_ARGUMENT;
+    RetrySettings retrySettings =
+        RetrySettings.newBuilder()
+            .setTotalTimeout(org.threeten.bp.Duration.ofMillis(5000L))
+            .setMaxAttempts(attempts)
+            .build();
+
+    OpenTelemetryTracingFactory tracingFactory = new OpenTelemetryTracingFactory(openTelemetrySdk);
+
+    EchoSettings httpJsonEchoSettings = createEchoSettings(true);
+    EchoStubSettings.Builder httpJsonEchoSettingsBuilder =
+        (EchoStubSettings.Builder) httpJsonEchoSettings.getStubSettings().toBuilder();
+    httpJsonEchoSettingsBuilder
+        .echoSettings()
+        .setRetrySettings(retrySettings)
+        .setRetryableCodes(statusCode);
+    httpJsonEchoSettingsBuilder.setTracerFactory(tracingFactory);
+    EchoStub stub = new ExtendedEchoStubSettings(httpJsonEchoSettingsBuilder).createStub();
+    EchoClient httpClient = EchoClient.create(stub);
+
+    EchoRequest echoRequest =
+        EchoRequest.newBuilder()
+            .setError(Status.newBuilder().setCode(statusCode.ordinal()).build())
+            .build();
+
+    Span parentSpan = tracer.spanBuilder("application-parent-operation").startSpan();
+    try (Scope scope = parentSpan.makeCurrent()) {
+      assertThrows(InvalidArgumentException.class, () -> httpClient.echo(echoRequest));
+    } finally {
+      parentSpan.end();
+    }
+
+    List<SpanData> spans = spanExporter.getFinishedSpanItems();
+    assertThat(spans).hasSize(attempts + 1);
+
+    SpanData rootSpan =
+        spans.stream()
+            .filter(span -> span.getName().equals("application-parent-operation"))
+            .findFirst()
+            .orElseThrow(() -> new AssertionError("Parent span not found"));
+
+    List<SpanData> attemptSpans =
+        spans.stream()
+            .filter(span -> span.getName().equals(SPAN_NAME_ECHO_HTTP))
+            .collect(java.util.stream.Collectors.toList());
+    assertThat(attemptSpans).hasSize(attempts);
+
+    for (SpanData attemptSpan : attemptSpans) {
+      assertThat(attemptSpan.getKind()).isEqualTo(SpanKind.CLIENT);
+      assertThat(attemptSpan.getParentSpanId()).isEqualTo(rootSpan.getSpanContext().getSpanId());
+      assertThat(attemptSpan.getSpanContext().getTraceId())
+          .isEqualTo(rootSpan.getSpanContext().getTraceId());
+    }
+  }
+
   private SpanData getErrorSpan() {
     Awaitility.await()
         .atMost(Duration.ofSeconds(5))