fix: histogram aggregator lastUpdateTime (#1567)

* chore: fix histogram aggregator update time

* chore: add tests and fix logic

* chore: fix lint

* fix: use sinon faketimers instead of sleep

packages/opentelemetry-metrics/src/export/aggregators/Histogram.ts

@@ -45,6 +45,7 @@ export class HistogramAggregator implements HistogramAggregatorType {
   }
 
   update(value: number): void {
+    this._lastUpdateTime = hrTime();
     this._current.count += 1;
     this._current.sum += value;
 
@@ -54,7 +55,6 @@ export class HistogramAggregator implements HistogramAggregatorType {
         return;
       }
     }
-
     // value is above all observed boundaries
     this._current.buckets.counts[this._boundaries.length] += 1;
   }

packages/opentelemetry-metrics/test/export/aggregators/Histogram.test.ts

@@ -17,6 +17,8 @@
 import * as assert from 'assert';
 import { HistogramAggregator } from '../../../src/export/aggregators';
 import { Histogram } from '../../../src';
+import { hrTime, hrTimeToMilliseconds } from '@opentelemetry/core';
+import sinon = require('sinon');
 
 describe('HistogramAggregator', () => {
   describe('constructor()', () => {
@@ -99,6 +101,30 @@ describe('HistogramAggregator', () => {
     });
   });
 
+  describe('.timestamp', () => {
+    let clock: sinon.SinonFakeTimers;
+    before(() => {
+      clock = sinon.useFakeTimers({ toFake: ['hrtime'] });
+    });
+
+    it('should update point timestamp', () => {
+      const aggregator = new HistogramAggregator([100, 200]);
+      const timestamp = hrTimeToMilliseconds(hrTime());
+      const timeDiff = 10;
+      clock.tick(timeDiff);
+      aggregator.update(150);
+      assert.equal(
+        hrTimeToMilliseconds(aggregator.toPoint().timestamp) >=
+          timestamp + timeDiff,
+        true
+      );
+    });
+
+    after(() => {
+      clock.restore();
+    });
+  });
+
   describe('.count', () => {
     it('should return last checkpoint count', () => {
       const aggregator = new HistogramAggregator([100]);