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src/server/__tests__/checkBrowserVersion-test.js

@@ -0,0 +1,61 @@
+jest.mock('child_process');
+const childProcess = require('child_process');
+
+jest.mock('../config');
+const config = require('../config');
+
+const checkBrowserVersion = require('../checkBrowserVersion');
+
+beforeEach(() => {
+  config.driver = 'firefox';
+});
+
+describe('when firefox is new enough', () => {
+  beforeEach(() => {
+    childProcess.exec = (_, cb) => cb(null, 'Mozilla Firefox 50.0');
+  });
+
+  it('resolves', () =>
+    checkBrowserVersion().then(() => {
+      expect(true).toBe(true);
+    }));
+});
+
+describe('when firefox is too old', () => {
+  beforeEach(() => {
+    childProcess.exec = (_, cb) => cb(null, 'Mozilla Firefox 47.0');
+  });
+
+  it('rejects', () =>
+    checkBrowserVersion().catch((error) => {
+      expect(error.message).toEqual(
+        'Happo requires Firefox version 50 or later. You are using 47.0');
+    }));
+});
+
+describe('when the version string is unrecognized', () => {
+  beforeEach(() => {
+    childProcess.exec = (_, cb) => cb(null, 'Godzilla Firefox 47.0');
+  });
+
+  it('rejects', () =>
+    checkBrowserVersion().catch((error) => {
+      expect(error.message).toEqual(
+        'Failed to parse Firefox version string "Godzilla Firefox 47.0"');
+    }));
+});
+
+describe('when using a different driver', () => {
+  beforeEach(() => {
+    config.driver = 'chrome';
+
+    // Just to make sure that we're not falsely succeeding because of normal
+    // handling, we also mock an old version of Firefox.
+    childProcess.exec = (_, cb) => cb(null, 'Mozilla Firefox 47.0');
+  });
+
+  it('resolves', () =>
+    checkBrowserVersion().then(() => {
+      expect(true).toBe(true);
+    }));
+});

src/server/__tests__/runVisualDiffs-test.js

@@ -8,6 +8,9 @@ const initializeWebdriver = require('../initializeWebdriver');
 const runVisualDiffs = require('../runVisualDiffs');
 const server = require('../server');
 
+jest.mock('../checkBrowserVersion');
+const checkBrowserVersion = require('../checkBrowserVersion');
+
 describe('runVisualDiffs', () => {
   let driver;
   let startedServer;
@@ -30,6 +33,7 @@ describe('runVisualDiffs', () => {
 
   beforeEach(() => {
     originalConfig = { ...config };
+    checkBrowserVersion.mockImplementation(() => Promise.resolve());
   });
 
   afterEach(() => {

src/server/checkBrowserVersion.js

@@ -0,0 +1,37 @@
+const childProcess = require('child_process');
+
+const firefox = require('selenium-webdriver/firefox');
+
+const config = require('./config');
+
+const MINIMUM_FIREFOX_VERSION = 50.0;
+const FIREFOX_VERSION_MATCHER = /Mozilla Firefox ([0-9.]+)/;
+
+module.exports = function checkBrowserVersion() {
+  if (config.driver !== 'firefox') {
+    // Our main browser target is Firefox. If you are using something else, you
+    // must know what you are doing. :)
+    return Promise.resolve();
+  }
+
+  return new Promise((resolve, reject) => {
+    new firefox.Binary().locate().then((pathToExecutable) => {
+      childProcess.exec(`${pathToExecutable} --version`, (error, stdout) => {
+        if (error) {
+          reject(new Error(`Failed to check Firefox version: ${error}`));
+          return;
+        }
+        const match = stdout.match(FIREFOX_VERSION_MATCHER);
+        if (!match) {
+          reject(new Error(`Failed to parse Firefox version string "${stdout}"`));
+        } else if (parseFloat(match[1]) < MINIMUM_FIREFOX_VERSION) {
+          reject(new Error(
+            `Happo requires Firefox version ${MINIMUM_FIREFOX_VERSION} or later. ` +
+            `You are using ${match[1]}`));
+        } else {
+          resolve();
+        }
+      });
+    });
+  });
+};

src/server/cli.js

@@ -3,6 +3,7 @@ const crypto = require('crypto');
 const commander = require('commander');
 
 const S3Uploader = require('./S3Uploader');
+const checkBrowserVersion = require('./checkBrowserVersion');
 const constructUrl = require('./constructUrl');
 const initializeWebdriver = require('./initializeWebdriver');
 const runVisualDiffs = require('./runVisualDiffs');
@@ -21,8 +22,10 @@ commander.command('debug').action(() => {
 });
 
 commander.command('run').action(() => {
-  server.start().then(() => {
-    initializeWebdriver().then((driver) => {
+  server.start()
+    .then(checkBrowserVersion)
+    .then(initializeWebdriver)
+    .then((driver) => {
       runVisualDiffs(driver)
         .then(() => {
           driver.close();
@@ -33,7 +36,6 @@ commander.command('run').action(() => {
           logAndExit(error);
         });
     });
-  });
 });
 
 commander.command('review').action(() => {