test(o11y): add tests to verify error.type extraction in metrics tracer

Added additional test cases to GoldenSignalsMetricsTracerTest to ensure that ObservabilityUtils.extractErrorType is correctly translating various exceptions (like CancellationException, SocketTimeoutException, and IllegalArgumentException) into the appropriate error.type attributes during failure reporting.

Author: blakeli0

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/GoldenSignalsMetricsTracerTest.java

@@ -168,4 +168,62 @@ void operationFailed_shouldRecordsOKStatus() {
                 AttributeKey.stringKey(RPC_RESPONSE_STATUS_ATTRIBUTE),
                 StatusCode.Code.INTERNAL.toString()));
   }
+
+  @Test
+  void operationFailed_shouldRecordCancellationException() {
+    java.util.concurrent.CancellationException error =
+        new java.util.concurrent.CancellationException("test cancellation");
+    tracer.operationFailed(error);
+
+    Collection<MetricData> metrics = metricReader.collectAllMetrics();
+    assertThat(metrics).hasSize(1);
+    MetricData metricData = metrics.iterator().next();
+
+    assertThat(metricData.getHistogramData().getPoints()).hasSize(1);
+    assertThat(metricData.getHistogramData().getPoints().iterator().next().getAttributes())
+        .isEqualTo(
+            Attributes.of(
+                AttributeKey.stringKey(ObservabilityAttributes.ERROR_TYPE_ATTRIBUTE),
+                "CancellationException",
+                AttributeKey.stringKey(RPC_RESPONSE_STATUS_ATTRIBUTE),
+                StatusCode.Code.CANCELLED.toString()));
+  }
+
+  @Test
+  void operationFailed_shouldRecordClientTimeout() {
+    java.net.SocketTimeoutException error = new java.net.SocketTimeoutException("test timeout");
+    tracer.operationFailed(error);
+
+    Collection<MetricData> metrics = metricReader.collectAllMetrics();
+    assertThat(metrics).hasSize(1);
+    MetricData metricData = metrics.iterator().next();
+
+    assertThat(metricData.getHistogramData().getPoints()).hasSize(1);
+    assertThat(metricData.getHistogramData().getPoints().iterator().next().getAttributes())
+        .isEqualTo(
+            Attributes.of(
+                AttributeKey.stringKey(ObservabilityAttributes.ERROR_TYPE_ATTRIBUTE),
+                "CLIENT_TIMEOUT",
+                AttributeKey.stringKey(RPC_RESPONSE_STATUS_ATTRIBUTE),
+                StatusCode.Code.UNKNOWN.toString()));
+  }
+
+  @Test
+  void operationFailed_shouldRecordClientRequestError() {
+    IllegalArgumentException error = new IllegalArgumentException("test illegal argument");
+    tracer.operationFailed(error);
+
+    Collection<MetricData> metrics = metricReader.collectAllMetrics();
+    assertThat(metrics).hasSize(1);
+    MetricData metricData = metrics.iterator().next();
+
+    assertThat(metricData.getHistogramData().getPoints()).hasSize(1);
+    assertThat(metricData.getHistogramData().getPoints().iterator().next().getAttributes())
+        .isEqualTo(
+            Attributes.of(
+                AttributeKey.stringKey(ObservabilityAttributes.ERROR_TYPE_ATTRIBUTE),
+                "CLIENT_REQUEST_ERROR",
+                AttributeKey.stringKey(RPC_RESPONSE_STATUS_ATTRIBUTE),
+                StatusCode.Code.UNKNOWN.toString()));
+  }
 }