Initial work on in-browser test runner

Run `grunt test` and open up the `build/test/index.html` to run the
tests.

src/js/test/TestRegister.js

@@ -0,0 +1,97 @@
+/**
+ * TestRegister.js
+ *
+ * This is so individual files can register their tests in one place, and
+ * ensure that they will get run by the frontend.
+ *
+ * @author tlwr [toby@toby.codes
+ *
+ * @copyright Crown Copyright 2017
+ * @license Apache-2.0
+ *
+ */
+(function() {
+    /**
+     * Add a list of tests to the register.
+     *
+     * @class
+     */
+    function TestRegister() {
+        this.tests = [];
+    }
+
+    /**
+     * Add a list of tests to the register.
+     *
+     * @param {Object[]} tests
+     */
+    TestRegister.prototype.addTests = function(tests) {
+        this.tests = this.tests.concat(tests.map(function(test) {
+
+            test.status = "waiting";
+            test.output = "";
+
+            return test;
+        }));
+    };
+
+    /**
+     * Returns the list of tests.
+     *
+     * @returns {Object[]} tests
+        return this.tests;
+    };
+
+    /**
+     * Runs all the tests in the register and updates the state of each test.
+     *
+     */
+    TestRegister.prototype.runTests = function() {
+        this.tests.forEach(function(test, i) {
+            var chef = new Chef();
+
+            // This resolve is to not instantly break when async operations are
+            // supported. Marked as TODO.
+            Promise.resolve(chef.bake(
+                test.input,
+                test.recipeConfig,
+                {},
+                0,
+                0
+            ))
+                .then(function(result) {
+                    if (result.error) {
+                        if (test.expectedError) {
+                            test.status = "passing";
+                        } else {
+                            test.status = "erroring";
+                            test.output = [
+                                "Erroring",
+                                "-------",
+                                result.error.displayStr,
+                            ].join("\n");
+                        }
+                    } else {
+                        if (result.result === test.expectedOutput) {
+                            test.status = "passing";
+                        } else {
+                            test.status = "failing";
+                            test.output = [
+                                "Failing",
+                                "-------",
+                                "Expected",
+                                "-------",
+                                test.expectedOutput,
+                                "Actual",
+                                "-------",
+                                result.result,
+                            ].join("\n");
+                        }
+                    }
+                });
+        });
+    };
+
+    // Singleton TestRegister, keeping things simple and obvious.
+    window.TestRegister = new TestRegister();
+})();