Add Node.js test asserting on the number of sourcemap comments in fin…

…al assets

tests/node/sourcemap-test.js

@@ -0,0 +1,27 @@
+var fs = require('fs');
+
+QUnit.module('sourcemap validation', function() {
+  var assets = ['ember.debug', 'ember.prod', 'ember.min'];
+
+  assets.forEach(asset => {
+    QUnit.test(`${asset} has only a single sourcemaps comment`, function(assert) {
+      var jsPath = `dist/${asset}.js`;
+      assert.ok(fs.existsSync(jsPath));
+
+      var contents = fs.readFileSync(jsPath, 'utf-8');
+      var num = count(contents, '//# sourceMappingURL=');
+      assert.equal(num, 1);
+    });
+  });
+});
+
+function count(source, find) {
+  var num = 0;
+
+  var i = -1;
+  while ((i = source.indexOf(find, i + 1)) !== -1) {
+    num += 1;
+  }
+
+  return num;
+}