Implement Instanbul test coverage for the electron-mocha tests

* Custom mocha reporter to pass results to Istanbul
* Istanbul reporter generates text and HTML reports

.eslintignore

@@ -1,2 +1,3 @@
 build/
 node_modules/
+cov/

.gitignore

@@ -1,6 +1,8 @@
 node_modules/
 build/
 dist/
+cov/
+coverage/
 .settings.json
 xunit.xml
 vendor/*.msi

package.json

@@ -26,8 +26,10 @@
     "postinstall": "node vendor/rebuild.js --instant",
     "test": "npm run lint",
     "pretest-electron": "npm run build",
+    "pretest-electron-coverage": "istanbul instrument src --output cov --no-compact --complete-copy --es-modules",
     "pretest-spectron": "npm run build",
-    "test-electron": "electron-mocha ./test/electron --recursive --compilers js:babel-core/register --timeout 10000 -R spec-xunit-file",
+    "test-electron": "electron-mocha ./test/electron/**/*_spec.js --recursive --compilers js:babel-core/register --timeout 10000 -R spec-xunit-file",
+    "test-electron-coverage": "npm run test-electron -- -r test/electron/util/coverage.js -R test/istanbul-reporter",
     "test-spectron": "mocha ./test/spectron --compilers js:babel-core/register -R spec-xunit-file --timeout 10000",
     "prestart": "pre-flight && node vendor/mac_patch_dev.js",
     "start": "electron . --dev",
@@ -94,6 +96,7 @@
     "gulp-less": "^3.1.0",
     "gulp-replace": "^0.5.4",
     "gulp-uglify": "^2.0.0",
+    "istanbul": "^1.1.0-alpha.1",
     "jquery": "^2.2.3",
     "material-design-icons-iconfont": "^2.0.5",
     "materialize-css": "^0.97.6",

test/electron/util/coverage.js

@@ -0,0 +1,11 @@
+import Module from 'module';
+
+const originalRequire = Module.prototype.require;
+
+Module.prototype.require = function fancyCoverageRequireHack(moduleName, ...args) {
+  try {
+    return originalRequire.call(this, moduleName.replace('build/', 'cov/'), ...args);
+  } catch (e) {
+    return originalRequire.call(this, moduleName, ...args);
+  }
+};

test/istanbul-reporter.js

@@ -0,0 +1,17 @@
+const istanbulAPI = require('istanbul-api');
+const libCoverage = require('istanbul-lib-coverage');
+
+function Istanbul(runner) {
+  runner.on('end', () => {
+    const mainReporter = istanbulAPI.createReporter();
+    const coverageMap = libCoverage.createCoverageMap();
+
+    coverageMap.merge(global.__coverage__ || {});
+
+    mainReporter.addAll(['text', 'html']);
+    mainReporter.write(coverageMap, {});
+  });
+}
+
+
+module.exports = Istanbul;