fix(watcher): use correct file sha in url query string

Use the most recently computed file sha present on the served file
when setting the file sha in the scripts tags added to the context.html.

This fixes an issue where the sha query arg would always be the sha of
the file when karma initially started and would not take into account
changes to the file when the watcher is running.

This may also address the issues in #2317 and #2264

lib/middleware/karma.js

@@ -11,6 +11,8 @@
  * - setting propert caching headers
  */
 
+var _ = require('lodash')
+var from = require('core-js/library/fn/array/from')
 var path = require('path')
 var util = require('util')
 var url = require('url')
@@ -74,6 +76,12 @@ var isFirefox = function (req) {
   return firefox
 }
 
+var findByPath = function (files, path) {
+  return _.find(from(files), function (file) {
+    return file.path === path
+  })
+}
+
 var createKarmaMiddleware = function (
   filesPromise,
   serveStaticFile,
@@ -183,7 +191,12 @@ var createKarmaMiddleware = function (
               filePath = filePathToUrlPath(filePath, basePath, urlRoot, proxyPath)
 
               if (requestUrl === '/context.html') {
-                filePath += '?' + file.sha
+                var servedFile = findByPath(files.served, file.path)
+                if (servedFile) {
+                  filePath += '?' + servedFile.sha
+                } else {
+                  filePath += '?' + file.sha
+                }
               }
             }
 

test/unit/middleware/karma.spec.js

@@ -239,6 +239,27 @@ describe('middleware.karma', () => {
     callHandlerWith('/__karma__/context.html')
   })
 
+  it('should serve the sha of the served file if the file is in served files', (done) => {
+    var include = [
+      new MockFile('/some/abc/a.js', 'sha1'),
+      new MockFile('/base/path/b.js', 'sha2')
+    ]
+
+    var serve = [
+      new MockFile('/some/abc/a.js', 'sha3'),
+      new MockFile('/base/path/b.js', 'sha4')
+    ]
+
+    filesDeferred.resolve({included: include, served: serve})
+
+    response.once('end', () => {
+      expect(response).to.beServedAs(200, 'CONTEXT\n<script type="text/javascript" src="/__proxy__/__karma__/absolute/some/abc/a.js?sha3" crossorigin="anonymous"></script>\n<script type="text/javascript" src="/__proxy__/__karma__/base/b.js?sha4" crossorigin="anonymous"></script>')
+      done()
+    })
+
+    callHandlerWith('/__karma__/context.html')
+  })
+
   it('should serve context.html with the correct path for link tags', (done) => {
     includedFiles([
       new MockFile('/some/abc/a.css', 'sha1'),