Add TTI < 10s audit for PWA

lighthouse-core/audits/load-fast-enough-for-pwa.js

@@ -0,0 +1,89 @@
+/**
+ * @license Copyright 2017 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+
+'use strict';
+
+/** @fileoverview
+ *  This audit evaluates if a page's load performance is fast enough for it to be considered a PWA.
+ *  We are doublechecking that the network requests were throttled (or slow on their own)
+ *  Afterwards, we report if the TTI is less than 10 seconds.
+ */
+
+const Audit = require('./audit');
+const TTIMetric = require('./time-to-interactive');
+const Emulation = require('../lib/emulation');
+
+const Formatter = require('../report/formatter');
+
+// Maximum TTI to be considered "fast" for PWA baseline checklist
+//   https://developers.google.com/web/progressive-web-apps/checklist
+const MAXIMUM_TTI = 10 * 1000;
+
+class LoadFastEnough4Pwa extends Audit {
+  /**
+   * @return {!AuditMeta}
+   */
+  static get meta() {
+    return {
+      category: 'PWA',
+      name: 'load-fast-enough-for-pwa',
+      description: 'Page load is fast enough on 3G',
+      helpText: 'Satisfied if the _Time To Interactive_ duration is shorter than _10 seconds_, as defined by the [PWA Baseline Checklist](https://developers.google.com/web/progressive-web-apps/checklist). Network throttling is required (specifically: RTT latencies >= 150 RTT are expected).',
+      requiredArtifacts: ['traces', 'networkRecords']
+    };
+  }
+
+  /**
+   * @param {!Artifacts} artifacts
+   * @return {!AuditResult}
+   */
+  static audit(artifacts) {
+    const networkRecords = artifacts.networkRecords[Audit.DEFAULT_PASS];
+    const allRequestLatencies = networkRecords.map(record => {
+      if (!record._timing) return Infinity;
+      // Use DevTools' definition of Waiting latency: https://github.com/ChromeDevTools/devtools-frontend/blob/66595b8a73a9c873ea7714205b828866630e9e82/front_end/network/RequestTimingView.js#L164
+      return record._timing.receiveHeadersEnd - record._timing.sendEnd;
+    });
+
+    const latency3gMin = Emulation.settings.TYPICAL_MOBILE_THROTTLING_METRICS.latency - 10;
+    const areLatenciesAll3G = allRequestLatencies.every(val => val > latency3gMin);
+
+    return TTIMetric.audit(artifacts).then(ttiResult => {
+      const timeToInteractive = ttiResult.extendedInfo.value.timings.timeToInteractive;
+      const isFast = timeToInteractive < MAXIMUM_TTI;
+
+      const extendedInfo = {
+        formatter: Formatter.SUPPORTED_FORMATS.NULL,
+        value: {areLatenciesAll3G, allRequestLatencies, isFast, timeToInteractive}
+      };
+
+      if (!areLatenciesAll3G) {
+        return {
+          rawValue: false,
+          // eslint-disable-next-line max-len
+          debugString: `The Time To Interactive was found at ${ttiResult.displayValue}, however, the network request latencies were not sufficiently realistic, so the performance measurements cannot be trusted.`,
+          extendedInfo
+        };
+      }
+
+      if (!isFast) {
+        return {
+          rawValue: false,
+           // eslint-disable-next-line max-len
+          debugString: `Under 3G conditions, the Time To Interactive was at ${ttiResult.displayValue}. More details in the "Performance" section.`,
+          extendedInfo
+        };
+      }
+
+      return {
+        rawValue: true,
+        extendedInfo
+      };
+    });
+  }
+}
+
+module.exports = LoadFastEnough4Pwa;

lighthouse-core/config/default.json

@@ -64,6 +64,7 @@
     "manifest-display",
     "without-javascript",
     "first-meaningful-paint",
+    "load-fast-enough-for-pwa",
     "speed-index-metric",
     "estimated-input-latency",
     "time-to-interactive",
@@ -134,6 +135,10 @@
       "name": "Page load performance is fast",
       "description": "Users notice if sites and apps don't perform well. These top-level metrics capture the most important perceived performance concerns.",
       "audits": {
+        "load-fast-enough-for-pwa": {
+          "expectedValue": true,
+          "weight": 1
+        },
         "first-meaningful-paint": {
           "expectedValue": 100,
           "weight": 1

lighthouse-core/lib/emulation.js

@@ -151,5 +151,14 @@ module.exports = {
   enableCPUThrottling,
   disableCPUThrottling,
   goOffline,
-  getEmulationDesc
+  getEmulationDesc,
+  settings: {
+    NEXUS5X_EMULATION_METRICS,
+    NEXUS5X_USERAGENT,
+    TYPICAL_MOBILE_THROTTLING_METRICS,
+    OFFLINE_METRICS,
+    NO_THROTTLING_METRICS,
+    NO_CPU_THROTTLE_METRICS,
+    CPU_THROTTLE_METRICS
+  }
 };

lighthouse-core/test/audits/load-fast-enough-for-pwa-test.js

@@ -0,0 +1,99 @@
+/**
+ * @license Copyright 2017 Google Inc. All Rights Reserved.
+ * 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 http://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.
+ */
+
+'use strict';
+
+const FastPWAAudit = require('../../audits/load-fast-enough-for-pwa');
+const TTIAudit = require('../../audits/time-to-interactive');
+const Audit = require('../../audits/audit.js');
+const assert = require('assert');
+
+function generateTTIResults(ttiValue) {
+  const ttiResult = {
+    rawValue: ttiValue,
+    extendedInfo: {
+      value: {
+        timings: {
+          timeToInteractive: ttiValue
+        }
+      }
+    }
+  };
+  return Promise.resolve.bind(Promise, ttiResult);
+}
+
+function generateArtifacts(networkRecords = []) {
+  return {
+    networkRecords: {
+      [Audit.DEFAULT_PASS]: networkRecords
+    },
+    traces: {
+      [Audit.DEFAULT_PASS]: {traceEvents: []}
+    }
+  };
+}
+
+/* eslint-env mocha */
+describe('PWA: load-fast-enough-for-pwa audit', () => {
+  // monkeypatch TTI to for a more focused test
+  let origTTI;
+  beforeEach(() => origTTI = TTIAudit.audit);
+  afterEach(() => TTIAudit.audit = origTTI);
+
+  it('returns boolean based on TTI value', () => {
+    TTIAudit.audit = generateTTIResults(5000);
+    return FastPWAAudit.audit(generateArtifacts()).then(result => {
+      assert.equal(result.rawValue, true, 'fixture trace is not passing audit');
+    }).catch(err => {
+      assert.ok(false, err);
+    });
+  });
+
+  it('fails a bad TTI value', () => {
+    TTIAudit.audit = generateTTIResults(15000);
+    return FastPWAAudit.audit(generateArtifacts()).then(result => {
+      assert.equal(result.rawValue, false, 'not failing a long TTI value');
+      assert.ok(result.debugString);
+    }).catch(err => {
+      assert.ok(false, err);
+    });
+  });
+
+  it('fails a good TTI value with no throttling', () => {
+    TTIAudit.audit = generateTTIResults(5000);
+    // latencies are very short
+    const mockNetworkRecords = [
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 50}},
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 75}},
+      { },
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 50}},
+    ];
+    return FastPWAAudit.audit(generateArtifacts(mockNetworkRecords)).then(result => {
+      assert.equal(result.rawValue, false);
+      assert.ok(result.debugString.includes('network request latencies'));
+    }).catch(err => {
+      assert.ok(false, err);
+    });
+  });
+
+
+  it('passes a good TTI value and WITH throttling', () => {
+    TTIAudit.audit = generateTTIResults(5000);
+    // latencies are very long
+    const mockNetworkRecords = [
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 250}},
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 175}},
+      { },
+      {_timing: {sendEnd: 0, receiveHeadersEnd: 250}},
+    ];
+    return FastPWAAudit.audit(generateArtifacts(mockNetworkRecords)).then(result => {
+      assert.equal(result.rawValue, true);
+      assert.strictEqual(result.debugString, undefined);
+    }).catch(err => {
+      assert.ok(false, err);
+    });
+  });
+});