i13n: Extract experiments module

... from the statsvInstrumentation module so that the bucketing logic
can be shared with other instrumentation modules.

Change-Id: I5732fa539a3911939fa85fa88c102fa8dcfa5613

src/experiments.js

@@ -0,0 +1,55 @@
+/**
+ * @module experiments
+ */
+
+/**
+ * @interface Experiments
+ *
+ * @global
+ */
+
+/**
+ * Creates a helper wrapper for the MediaWiki-provided
+ * `mw.experiments#getBucket` bucketing function.
+ *
+ * @param {mw.experiments} mwExperiments The `mw.experiments` singleton instance
+ * @return {Experiments}
+ */
+module.exports = function createExperiments( mwExperiments ) {
+	return {
+
+		/**
+		 * Gets whether something is true given a name and a token.
+		 *
+		 * @example
+		 * const experiments = require( './src/experiments' )( mw.experiments );
+		 * const isFooEnabled = experiments.weightedBoolean(
+		 *   'foo',
+		 *   10 / 100, // 10% of all unique tokens should have foo enabled.
+		 *   token
+		 * );
+		 *
+		 * @function
+		 * @name Experiments#weightedBoolean
+		 * @param {String} name The name of the thing. Since this is used as the
+		 *  name of the underlying experiment it should be unique to reduce the
+		 *  likelihood of collisions with other enabled experiments
+		 * @param {Number} trueWeight A number between 0 and 1, representing the
+		 *  probability of the thing being true
+		 * @param {String} token A token associated with the user for the duration
+		 *  of the experiment
+		 * @return {Boolean}
+		 */
+		weightedBoolean: function ( name, trueWeight, token ) {
+			return mwExperiments.getBucket( {
+				enabled: true,
+
+				name: name,
+				buckets: {
+					'true': trueWeight,
+					'false': 1 - trueWeight
+				}
+			}, token ) === 'true';
+		}
+	};
+};

src/index.js

@@ -17,6 +17,7 @@ var mw = mediaWiki,
 	createIsEnabled = require( './isEnabled' ),
 	title = require( './title' ),
 	renderer = require( './renderer' ),
+	createExperiments = require( './experiments' ),
 	statsvInstrumentation = require( './statsvInstrumentation' ),
 
 	changeListeners = require( './changeListeners' ),
@@ -116,6 +117,7 @@ mw.requestIdleCallback( function () {
 		gateway = createGateway( mw.config ),
 		userSettings,
 		settingsDialog,
+		experiments,
 		statsvTracker,
 		isEnabled,
 		schema,
@@ -123,7 +125,8 @@ mw.requestIdleCallback( function () {
 
 	userSettings = createUserSettings( mw.storage );
 	settingsDialog = createSettingsDialogRenderer();
-	statsvTracker = getStatsvTracker( mw.user, mw.config, mw.experiments );
+	experiments = createExperiments( mw.experiments );
+	statsvTracker = getStatsvTracker( mw.user, mw.config, experiments );
 
 	isEnabled = createIsEnabled( mw.user, userSettings, mw.config, mw.experiments );
 

src/statsvInstrumentation.js

@@ -4,26 +4,22 @@
 
 /**
  * Gets whether Graphite logging (via [the statsv HTTP endpoint][0]) is enabled
- * for duration of the browser session. The sampling rate is controlled by
+ * for the duration of the user's session. The bucketing rate is controlled by
  * `wgPopupsStatsvSamplingRate`.
  *
  * [0]: https://wikitech.wikimedia.org/wiki/Graphite#statsv
  *
  * @param {mw.user} user The `mw.user` singleton instance
  * @param {mw.Map} config The `mw.config` singleton instance
- * @param {mw.experiments} experiments The `mw.experiments` singleton instance
+ * @param {Experiments} experiments
  * @returns {Boolean}
  */
 exports.isEnabled = function isEnabled( user, config, experiments ) {
-	var samplingRate = config.get( 'wgPopupsStatsvSamplingRate', 0 ),
-		bucket = experiments.getBucket( {
-			name: 'ext.Popups.statsv',
-			enabled: true,
-			buckets: {
-				control: 1 - samplingRate,
-				A: samplingRate
-			}
-		}, user.sessionId() );
+	var bucketingRate = config.get( 'wgPopupsStatsvSamplingRate', 0 );
 
-	return bucket === 'A';
+	return experiments.weightedBoolean(
+		'ext.Popups.statsv',
+		bucketingRate,
+		user.sessionId()
+	);
 };

tests/node-qunit/experiments.test.js

@@ -0,0 +1,39 @@
+var createExperiments = require( '../../src/experiments' );
+
+QUnit.module( 'ext.popups/experiments#weightedBoolean' );
+
+QUnit.test( 'it should call mw.experiments#getBucket', function ( assert ) {
+	var getBucketStub = this.sandbox.stub(),
+		stubMWExperiments = {
+			getBucket: getBucketStub
+		},
+		experiments = createExperiments( stubMWExperiments );
+
+	experiments.weightedBoolean( 'foo', 0.2, 'barbaz' );
+
+	assert.ok( getBucketStub.calledOnce );
+	assert.deepEqual(
+		getBucketStub.getCall( 0 ).args,
+		[
+			{
+				enabled: true,
+
+				name: 'foo',
+				buckets: {
+					'true': 0.2,
+					'false': 0.8 // 1 - 0.2
+				}
+			},
+			'barbaz'
+		]
+	);
+
+	// ---
+
+	getBucketStub.returns( 'true' );
+
+	assert.ok(
+		experiments.weightedBoolean( 'foo', 0.2, 'barbaz' ),
+		'It should return true if the bucket is "true".'
+	);
+} );

tests/node-qunit/statsvInstrumentation.test.js

@@ -1,27 +1,39 @@
 var stubs = require( './stubs' ),
 	statsv = require( '../../src/statsvInstrumentation' );
 
-QUnit.module( 'ext.popups/statsvInstrumentation', {
-	beforeEach: function () {
-		this.user = stubs.createStubUser();
-		this.config = stubs.createStubMap();
-	}
-} );
+QUnit.module( 'ext.popups/statsvInstrumentation' );
 
-QUnit.test( 'isEnabled', function ( assert ) {
-	var experiments = stubs.createStubExperiments( true );
+QUnit.test( '#isEnabled', function ( assert ) {
+	var user = stubs.createStubUser(),
+		config = stubs.createStubMap(),
+		weightedBooleanStub = this.sandbox.stub(),
+		experiments = {
+			weightedBoolean: weightedBooleanStub
+		};
 
-	assert.expect( 2 );
+	config.set( 'wgPopupsStatsvSamplingRate', 0.3141 );
 
-	assert.ok(
-		statsv.isEnabled( this.user, this.config, experiments ),
-		'Logging is enabled when the user is in the sample.'
+	statsv.isEnabled( user, config, experiments );
+
+	assert.ok( weightedBooleanStub.calledOnce );
+	assert.deepEqual(
+		weightedBooleanStub.getCall( 0 ).args,
+		[
+			'ext.Popups.statsv',
+			config.get( 'wgPopupsStatsvSamplingRate' ),
+			user.sessionId()
+		]
 	);
 
-	experiments = stubs.createStubExperiments( false );
+	// ---
 
-	assert.notOk(
-		statsv.isEnabled( this.user, this.config, experiments ),
-		'Logging is disabled when the user is not in the sample.'
+	config.delete( 'wgPopupsStatsvSamplingRate' );
+
+	statsv.isEnabled( user, config, experiments );
+
+	assert.deepEqual(
+		weightedBooleanStub.getCall( 1 ).args[ 1 ],
+		0,
+		'The bucketing rate should be 0 by default.'
 	);
 } );