Diagnostics: Add helper class for fake async methods

- Maintains a mapping of fake methods, resolvers and fake data

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: Ic07ddfc300679611b4d8dc908bb61a30631e9874
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2417450
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808543}

chrome/test/data/webui/chromeos/diagnostics/diagnostics_test.js

@@ -7,8 +7,48 @@ import 'chrome://resources/mojo/mojo/public/js/mojo_bindings_lite.js';
 import 'chrome://diagnostics/diagnostics_app.js';
 
 import {SystemDataProviderInterface} from 'chrome://diagnostics/diagnostics_types.js';
+import {FakeMethodResolver} from 'chrome://diagnostics/fake_method_resolver.js';
 import {getSystemDataProvider, setSystemDataProviderForTesting} from 'chrome://diagnostics/mojo_interface_provider.js';
 
+suite('DiagnosticsFakeMethodResolver', () => {
+  /** @type {?FakeMethodResolver} */
+  let resolver = null;
+
+  setup(function() {
+    resolver = new FakeMethodResolver();
+  });
+
+  teardown(function() {
+    resolver = null;
+  });
+
+  test('AddingMethodNoResult', () => {
+    resolver.register('foo');
+    return resolver.resolveMethod('foo').then((result) => {
+      assertEquals(undefined, result);
+    });
+  });
+
+  test('AddingMethodWithResult', () => {
+    resolver.register('foo');
+    const expected = {'foo': 'bar'};
+    resolver.setResult('foo', expected);
+    return resolver.resolveMethod('foo').then((result) => {
+      assertEquals(expected, result);
+    });
+  });
+
+  test('AddingTwoMethodCallingOne', () => {
+    resolver.register('foo');
+    resolver.register('bar');
+    const expected = {'fooKey': 'fooValue'};
+    resolver.setResult('foo', expected);
+    return resolver.resolveMethod('foo').then((result) => {
+      assertEquals(expected, result);
+    });
+  });
+});
+
 suite('DiagnosticsAppTest', () => {
   /** @type {?DiagnosticsApp} */
   let page = null;

chromeos/components/diagnostics_ui/resources/BUILD.gn

@@ -13,6 +13,7 @@ js_type_check("closure_compile_module") {
     ":diagnostics_app",
     ":diagnostics_card",
     ":diagnostics_types",
+    ":fake_method_resolver",
     ":mojo_interface_provider",
   ]
 }
@@ -33,6 +34,10 @@ js_library("diagnostics_card") {
 js_library("diagnostics_types") {
 }
 
+js_library("fake_method_resolver") {
+  deps = [ "//ui/webui/resources/js:cr.m" ]
+}
+
 js_library("mojo_interface_provider") {
   deps = [ "//ui/webui/resources/js:cr.m" ]
 }

chromeos/components/diagnostics_ui/resources/diagnostics_app_resources.grd

@@ -16,6 +16,7 @@
       <include name="IDR_DIAGNOSTICS_APP_ICON" file="app_icon_192.png" type="BINDATA" />
       <include name="IDR_DIAGNOSTICS_APP_INDEX_HTML" file="index.html" type="BINDATA" />
       <include name="IDR_DIAGNOSTICS_APP_JS" file="${root_gen_dir}/chromeos/components/diagnostics_ui/resources/diagnostics_app.js" use_base_dir="false" type="BINDATA"/>
+      <include name="IDR_DIAGNOSTICS_FAKE_METHOD_RESOLVER_JS" file="fake_method_resolver.js" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_MOJO_INTERFACE_PROVIDER_JS" file="mojo_interface_provider.js" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_SHARED_CSS_JS" file="${root_gen_dir}/chromeos/components/diagnostics_ui/resources/diagnostics_shared_css.js" use_base_dir="false" type="BINDDATA"/>
       <include name="IDR_DIAGNOSTICS_TYPES_JS" file="diagnostics_types.js" type="BINDATA"/>

chromeos/components/diagnostics_ui/resources/fake_method_resolver.js

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import {assert} from 'chrome://resources/js/assert.m.js';
+import {PromiseResolver} from 'chrome://resources/js/promise_resolver.m.js';
+
+/**
+ * @fileoverview
+ * Implements a helper class for managing a fake API with async
+ * methods.
+ */
+
+/**
+ * Maintains a resolver and the return value of the fake method.
+ * @template T
+ */
+class FakeMethodState {
+  constructor() {
+    /** @private {PromiseResolver} */
+    this.resolver_ = new PromiseResolver();
+
+    /** @private {T} */
+    this.result_ = undefined;
+  }
+
+  /**
+   * Resolve the method with the supplied result.
+   * @return {!Promise}
+   */
+  resolveMethod() {
+    this.resolver_.resolve(this.result_);
+    return this.resolver_.promise;
+  }
+
+  /**
+   * Set the result for this method.
+   * @param {T} result
+   */
+  setResult(result) {
+    this.result_ = result;
+  }
+}
+
+/**
+ * Manages a map of fake async methods, their resolvers and the fake
+ * return value they will produce.
+ * @template T
+ **/
+export class FakeMethodResolver {
+  constructor() {
+    /** @private {!Map<string, !FakeMethodState>} */
+    this.methodMap_ = new Map();
+  }
+
+  /**
+   * Registers methodName with the resolver. Calling other methods with a
+   * methodName that has not been registered will assert.
+   * @param {string} methodName
+   */
+  register(methodName) {
+    this.methodMap_.set(methodName, new FakeMethodState());
+  }
+
+  /**
+   * Set the value that methodName will produce when it resolves.
+   * @param {string} methodName
+   * @param {T} result
+   */
+  setResult(methodName, result) {
+    this.getState_(methodName).setResult(result);
+  }
+
+  /**
+   * Causes the promise for methodName to resolve.
+   * @param {string} methodName
+   * @return {!Promise}
+   */
+  resolveMethod(methodName) {
+    return this.getState_(methodName).resolveMethod();
+  }
+
+  /**
+   * Return the FakeMethodState for methodName.
+   * @param {string} methodName
+   * @return {!FakeMethodState}
+   * @private
+   */
+  getState_(methodName) {
+    const state = this.methodMap_.get(methodName);
+    assert(!!state, `Method '${methodName}' not found.`);
+    return state;
+  }
+}