[5/7] Telemetry Export: DatabricksTelemetryExporter with Retry and Circuit Breaker

tests/unit/.stubs/TelemetryExporterStub.ts

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+/**
+ * Copyright (c) 2025 Databricks Contributors
+ *
+ * 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
+ *
+ *     http://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.
+ */
+
+import { TelemetryMetric } from '../../../lib/telemetry/types';
+
+/**
+ * Stub implementation of DatabricksTelemetryExporter for testing.
+ * Records exported metrics for verification in tests.
+ */
+export default class TelemetryExporterStub {
+  public exportedMetrics: TelemetryMetric[][] = [];
+  public exportCount = 0;
+  public shouldThrow = false;
+  public throwError: Error | null = null;
+
+  /**
+   * Stub export method that records metrics.
+   */
+  async export(metrics: TelemetryMetric[]): Promise<void> {
+    this.exportCount++;
+    this.exportedMetrics.push([...metrics]);
+
+    if (this.shouldThrow && this.throwError) {
+      throw this.throwError;
+    }
+  }
+
+  /**
+   * Reset the stub state.
+   */
+  reset(): void {
+    this.exportedMetrics = [];
+    this.exportCount = 0;
+    this.shouldThrow = false;
+    this.throwError = null;
+  }
+
+  /**
+   * Get all exported metrics flattened.
+   */
+  getAllExportedMetrics(): TelemetryMetric[] {
+    return this.exportedMetrics.flat();
+  }
+
+  /**
+   * Configure stub to throw an error on export.
+   */
+  throwOnExport(error: Error): void {
+    this.shouldThrow = true;
+    this.throwError = error;
+  }
+}