feat(core-testing): RecordingMetrics test double

packages/core-testing/src/instrumentation/recording-metrics.ts

@@ -0,0 +1,66 @@
+// Local type alias matching the contract in @repo/core-shared/instrumentation.
+// Kept inline to avoid a build-graph cycle between core-testing and core-shared.
+type MetricAttributeValue = string | number | boolean;
+
+interface IMetrics {
+  counter(
+    name: string,
+    value?: number,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void;
+  histogram(
+    name: string,
+    value: number,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void;
+  gauge(
+    name: string,
+    value: number,
+    attributes?: Record<string, MetricAttributeValue>,
+  ): void;
+}
+
+export type RecordedMetric = {
+  kind: "counter" | "histogram" | "gauge";
+  name: string;
+  value: number;
+  attributes: Record<string, MetricAttributeValue>;
+};
+
+export class RecordingMetrics implements IMetrics {
+  metrics: RecordedMetric[] = [];
+
+  counter(
+    name: string,
+    value = 1,
+    attributes: Record<string, MetricAttributeValue> = {},
+  ): void {
+    this.metrics.push({ kind: "counter", name, value, attributes });
+  }
+
+  histogram(
+    name: string,
+    value: number,
+    attributes: Record<string, MetricAttributeValue> = {},
+  ): void {
+    this.metrics.push({ kind: "histogram", name, value, attributes });
+  }
+
+  gauge(
+    name: string,
+    value: number,
+    attributes: Record<string, MetricAttributeValue> = {},
+  ): void {
+    this.metrics.push({ kind: "gauge", name, value, attributes });
+  }
+
+  reset(): void {
+    this.metrics = [];
+  }
+
+  find(
+    predicate: (m: RecordedMetric) => boolean,
+  ): RecordedMetric | undefined {
+    return this.metrics.find(predicate);
+  }
+}