Extract chrome-launcher to a standalone thing.

ref #2092

chrome-launcher/test/global-mocha-hooks.js

@@ -0,0 +1,40 @@
+'use strict';
+
+const assert = require('assert');
+
+/**
+ * THIS FILE IS A DUPLICATE OF lighthouse-core/test/global-mocha-hooks.js
+ * Please keep them in sync.
+ */
+
+/* eslint-env mocha */
+let currTest;
+
+// monkey-patch all assert.* methods
+Object.keys(assert)
+  .filter(key => typeof assert[key] === 'function')
+  .forEach(key => {
+    const _origFn = assert[key];
+    assert[key] = function(...args) {
+      if (currTest) {
+        currTest._assertions++;
+      }
+      return _origFn.apply(this, args);
+    };
+  }
+);
+
+// store the count of assertions on each test's state object
+beforeEach(function() {
+  // eslint-disable-next-line no-invalid-this
+  currTest = this.currentTest;
+  currTest._assertions = currTest._assertions || 0;
+});
+
+afterEach(function() {
+  if (currTest._assertions === 0) {
+    throw new Error(`ZERO assertions in test: "${currTest.title}"\n${currTest.file}`);
+  }
+  currTest = null;
+});
+