test: moving average should not decay without new data (#1141)

This tests #1137

package.json

@@ -70,6 +70,7 @@
   },
   "devDependencies": {
     "@rollup/plugin-replace": "^2.3.4",
+    "@rollup/plugin-strip": "^2.0.1",
     "@videojs/generator-helpers": "~2.0.1",
     "d3": "^3.4.8",
     "es5-shim": "^4.5.13",

scripts/rollup.config.js

@@ -3,6 +3,7 @@ const worker = require('rollup-plugin-worker-factory');
 const {terser} = require('rollup-plugin-terser');
 const createTestData = require('./create-test-data.js');
 const replace = require('@rollup/plugin-replace');
+const strip = require('@rollup/plugin-strip');
 
 const CI_TEST_TYPE = process.env.CI_TEST_TYPE || '';
 
@@ -57,6 +58,9 @@ const options = {
     }
     defaults.module.unshift('replace');
 
+    defaults.module.unshift('strip');
+    defaults.browser.unshift('strip');
+
     return defaults;
   },
   primedPlugins(defaults) {
@@ -71,6 +75,9 @@ const options = {
         output: {comments: 'some'},
         compress: {passes: 2}
       }),
+      strip: strip({
+        functions: ['TEST_ONLY_*']
+      }),
       createTestData: createTestData()
     });
 

src/playlist-selectors.js

@@ -149,7 +149,7 @@ export const comparePlaylistResolution = function(left, right) {
  * currently detected bandwidth, accounting for some amount of
  * bandwidth variance
  */
-export const simpleSelector = function(
+export let simpleSelector = function(
   master,
   playerBandwidth,
   playerWidth,
@@ -313,6 +313,16 @@ export const simpleSelector = function(
   return null;
 };
 
+export const TEST_ONLY_SIMPLE_SELECTOR = (newSimpleSelector) => {
+  const oldSimpleSelector = simpleSelector;
+
+  simpleSelector = newSimpleSelector;
+
+  return function resetSimpleSelector() {
+    simpleSelector = oldSimpleSelector;
+  };
+};
+
 // Playlist Selectors
 
 /**

test/playlist-selectors.test.js

@@ -1,6 +1,7 @@
 import { module, test } from 'qunit';
 import document from 'global/document';
 import {
+  TEST_ONLY_SIMPLE_SELECTOR,
   simpleSelector,
   movingAverageBandwidthSelector,
   minRebufferMaxBandwidthSelector,
@@ -64,6 +65,50 @@ test('Exponential moving average has a configurable decay parameter', function(a
   assert.equal(playlist.attributes.BANDWIDTH, 50, 'selected the middle playlist');
 });
 
+test('Calling exponential moving average wont decay average unless new bandwidth data was provided', function(assert) {
+  let playlist;
+  const simSel = simpleSelector;
+  const bandwidthAverages = [];
+
+  const resetSimpleSelector = TEST_ONLY_SIMPLE_SELECTOR((...args) => {
+    // second argument to simpleSelector is the average
+    bandwidthAverages.push(args[1]);
+    return simSel(...args);
+  });
+
+  this.vhs.playlists.master.playlists = [
+    { attributes: { BANDWIDTH: 1 } },
+    { attributes: { BANDWIDTH: 50 } },
+    { attributes: { BANDWIDTH: 100 } }
+  ];
+
+  const fiftyPercentDecay = movingAverageBandwidthSelector(0.50);
+
+  this.vhs.systemBandwidth = 50 * Config.BANDWIDTH_VARIANCE + 1;
+  playlist = fiftyPercentDecay.call(this.vhs);
+  assert.equal(playlist.attributes.BANDWIDTH, 50, 'selected the middle playlist');
+
+  this.vhs.systemBandwidth = 1000 * Config.BANDWIDTH_VARIANCE + 1;
+  playlist = fiftyPercentDecay.call(this.vhs);
+  assert.equal(playlist.attributes.BANDWIDTH, 100, 'selected the top playlist');
+
+  // using the systemBandwidth values above, 50->1000
+  // we decay into 1000 after 50 iterations
+  let i = 50;
+
+  while (i--) {
+    playlist = fiftyPercentDecay.call(this.vhs);
+  }
+
+  assert.equal(
+    bandwidthAverages[bandwidthAverages.length - 1],
+    bandwidthAverages[1],
+    'bandwidth should only change when we get new bandwidth data'
+  );
+
+  resetSimpleSelector();
+});
+
 test(
   'minRebufferMaxBandwidthSelector picks highest rendition without rebuffering',
   function(assert) {