Start time bug in cumulative ExponentialHistogram

packages/sdk-metrics/test/regression/cumulative-exponential-histogram.test.ts

@@ -0,0 +1,90 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ *
+ * 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
+ *
+ *      https://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 * as assert from 'assert';
+import * as sinon from 'sinon';
+import {
+  Aggregation,
+  AggregationTemporality,
+  InstrumentType,
+  MeterProvider,
+  MetricReader,
+} from '../../src';
+import { TestMetricReader } from '../export/TestMetricReader';
+
+describe('cumulative-exponential-histogram', () => {
+  let clock: sinon.SinonFakeTimers;
+
+  beforeEach(() => {
+    clock = sinon.useFakeTimers();
+  });
+  afterEach(() => {
+    sinon.restore();
+  });
+
+  it('Cumulative Histogram should have the same startTime every collection', async () => {
+    // Works fine and passes
+    await doTest(Aggregation.Histogram());
+  });
+
+  it('Cumulative ExponentialHistogram should have the same startTime every collection', async () => {
+    // Fails
+    await doTest(Aggregation.ExponentialHistogram());
+  });
+
+  const doTest = async (histogramAggregation: Aggregation) => {
+    const meterProvider = new MeterProvider();
+    const reader = new TestMetricReader({
+      aggregationTemporalitySelector() {
+        return AggregationTemporality.CUMULATIVE;
+      },
+      aggregationSelector(type) {
+        return type === InstrumentType.HISTOGRAM
+          ? histogramAggregation
+          : Aggregation.Default();
+      },
+    });
+
+    meterProvider.addMetricReader(reader);
+    const meter = meterProvider.getMeter('my-meter');
+    const hist = meter.createHistogram('testhist');
+
+    hist.record(1);
+
+    const resourceMetrics1 = await collectNoErrors(reader);
+    const dataPoint1 =
+      resourceMetrics1.scopeMetrics[0].metrics[0].dataPoints[0];
+
+    clock.tick(1000);
+    hist.record(2);
+
+    const resourceMetrics2 = await collectNoErrors(reader);
+    const dataPoint2 =
+      resourceMetrics2.scopeMetrics[0].metrics[0].dataPoints[0];
+
+    assert.deepStrictEqual(
+      dataPoint1.startTime,
+      dataPoint2.startTime,
+      'The start time should be the same across cumulative collections'
+    );
+  };
+
+  const collectNoErrors = async (reader: MetricReader) => {
+    const { resourceMetrics, errors } = await reader.collect();
+    assert.strictEqual(errors.length, 0);
+    return resourceMetrics;
+  };
+});