Add ability to run tests with coverage report

spec/coverage/instrument.js

@@ -22,7 +22,7 @@ glob.sync('**/*.js', {cwd: libPath}).forEach(function (relativePath) {
   fs.writeFileSync(generatedPath, generated)
 })
 
-var asarPath = path.join(outputPath, 'electron-instrumented.asar')
+var asarPath = path.join(outputPath, 'electron.asar')
 asar.createPackageWithOptions(path.join(outputPath, 'lib'), asarPath, {}, function (error) {
   if (error) {
     console.error(error.stack || error)

spec/coverage/reporter.js

@@ -0,0 +1,51 @@
+const asar = require('asar')
+const fs = require('fs')
+const glob = require('glob')
+const mkdirp = require('mkdirp')
+const path = require('path')
+const {Collector, Instrumenter, Reporter} = require('istanbul')
+
+const outputPath = path.join(__dirname, '..', '..', 'out', 'coverage')
+const libPath = path.join(__dirname, '..', '..', 'lib')
+
+// Add unrequired files to the coverage report so all files are present there
+const addUnrequiredFiles = (coverage) => {
+  const instrumenter = new Instrumenter()
+  const libPath = path.join(__dirname, '..', '..', 'lib')
+
+  glob.sync('**/*.js', {cwd: libPath}).map(function (relativePath) {
+    return path.join(libPath, relativePath)
+  }).filter(function (filePath) {
+    return coverage[filePath] == null
+  }).forEach(function (filePath) {
+    instrumenter.instrumentSync(fs.readFileSync(filePath, 'utf8'), filePath)
+
+    // When instrumenting the code, istanbul will give each FunctionDeclaration
+    // a value of 1 in coverState.s,presumably to compensate for function
+    // hoisting. We need to reset this, as the function was not hoisted, as it
+    // was never loaded.
+    Object.keys(instrumenter.coverState.s).forEach(function (key) {
+        instrumenter.coverState.s[key] = 0
+    });
+
+    coverage[filePath] = instrumenter.coverState
+  })
+}
+
+// Generate a code coverage report in out/coverage/lcov-report
+exports.generateReport = () => {
+  const coverage = window.__coverage__
+  if (coverage == null) return
+
+  addUnrequiredFiles(coverage)
+
+  const collector = new Collector()
+  collector.add(coverage)
+
+  const {ipcRenderer} = require('electron')
+  collector.add(ipcRenderer.sendSync('get-coverage'))
+
+  const reporter = new Reporter(null, outputPath)
+  reporter.addAll(['text', 'lcov'])
+  reporter.write(collector, true, function () {})
+}