Add code coverage stats

Electron-mocha makes things like this a little difficult.  Luckily,
@inukshuk in
jprichardson/electron-mocha#19 (comment)
figures out a way to get around it. It's a bit of effort but does work
in the end.

With any luck an npm module will come out with these clues embedded in
it and the coverage.js can be removed.

.gitignore

@@ -1 +1,2 @@
 node_modules/
+coverage/

package.json

@@ -5,7 +5,8 @@
   "main": "index.js",
   "scripts": {
     "test": "electron-mocha",
-    "testmon": "nodemon --exec '(electron-mocha && growlnotify -n nodemon --image ~/green.png -m good) || (growlnotify -n nodemon --image ~/red.png -m crash && exit 1)'"
+    "testmon": "nodemon --exec '(electron-mocha && growlnotify -n nodemon --image ~/green.png -m good) || (growlnotify -n nodemon --image ~/red.png -m crash && exit 1)'",
+    "coverage": "electron-mocha --require test/coverage && istanbul report lcov"
   },
   "bin": {
     "scan": "./bin/scan"
@@ -14,8 +15,10 @@
   "license": "ISC",
   "devDependencies": {
     "chai": "^3.5.0",
+    "coveralls": "^2.11.9",
     "electron-mocha": "^2.3.0",
     "express": "^4.14.0",
+    "istanbul": "^0.4.4",
     "mocha": "^2.5.3",
     "nodemon": "^1.9.2"
   },

test/coverage.js

@@ -0,0 +1,57 @@
+'use strict'
+
+// Largely cribbed from
+// https://raw.githubusercontent.com/tropy/tropy/master/test/support/coverage.js
+
+const glob = require('glob')
+const { readFileSync: read, realpathSync } = require('fs')
+const { Reporter, Instrumenter, Collector, hook } = require('istanbul')
+const { keys } = Object
+
+function match () {
+  const map = {}
+  const fn = function (file) { return map[file] }
+  fn.files = []
+
+  for (let file of glob.sync(pattern)) {
+    let fullpath = realpathSync(file)
+    fn.files.push(fullpath)
+    map[fullpath] = true
+  }
+
+  return fn
+}
+
+function report () {
+  const cov = global.__coverage__
+  for (let file of matched.files) {
+    if (!cov[file]) {
+      // Add uncovered files to the report.
+      transformer(read(file, 'utf-8'), file)
+      for (let key of keys(instrumenter.coverState.s)) {
+        instrumenter.coverState.s[key] = 0
+      }
+      cov[file] = instrumenter.coverState
+    }
+  }
+
+  const collector = new Collector()
+  collector.add(cov)
+
+  const reporter = new Reporter()
+  reporter.addAll(['text-summary', 'json'])
+  reporter.write(collector, true, () => {})
+}
+
+// The source files to cover.  Avoid node_modules/, coverage/, and
+// */coverage.js (supposed to be test/coverage.js)
+
+const pattern = '{!(node_modules|coverage)/**,.}/!(coverage).js'
+const matched = match()
+
+const instrumenter = new Instrumenter()
+const transformer = instrumenter.instrumentSync.bind(instrumenter)
+
+hook.hookRequire(matched, transformer, {})
+
+process.on('exit', report)