Capacitor プラグインをモックする
アプリケーション内でユニットテストを作成する場合、 テスト対象のユニットに対する外部依存関係のモックを作成するのがベストプラクティスです。これには、コンポーネントやサービスが使用している Capacitor プラグインも含まれます。
ほとんどのモッキングライブラリは、オブジェクトを取得して JavaScript プロキシでラップすることでモックを作成し、そのオブジェクト上のメソッドの呼び出しを調べたりメソッドの戻り値を制御したりします。しかし、CapacitorプラグインはJavaScriptレイヤーの中でプロキシとして実装されています。プロキシのプロキシを作成することはサポートされておらず、失敗します。この問題を回避するために、手動モックを使用することができます。
手動モック
手動モックを使用すると、JavaScript モジュール全体の機能を簡単にスタブ化することができます。その結果、テストが import { Storage } from '@capacitor/storage' を実行すると、本当の Storage JavaScript proxy object をロードする代わりに、以下のようなものをロードすることになります。
export const Storage = {
async get(data: { key: string }): Promise<{ value: string | undefined }> {
return { value: undefined };
},
async set(data: { key: string; value: string }): Promise<void> {},
async clear(): Promise<void> {},
};
Since this is a plain JavaScript object and not a proxy object, it is very easy to spy on. Also, since it is a mock it does not try to make any native calls. This makes the use of manual mocks an ideal choice to use when testing code that uses Capacitor plugins.
Jest
The Jest testing framework has manual mocks built in to it. Create a __mocks__/@capacitor folder at the root of your project, and Jest will automatically load files from there rather than from node_modules.
For example, let's say you have the following directory structure:
.
|
+- __mocks__
| |
| +- @capacitor
| |
| +- storage.ts
| +- toast.ts
...
+- src
Your tests will use the stubs defined in storage.ts and toast.ts rather than the real @capacitor/storage and @capacitor/toast plugins from node_modules.
Jasmine
The Jasmine testing framework does not include the concept of "manual mocks" but we can easily simulate this through the use of TypeScript path mapping.
First, create the same directory structure at the root level of your project just like you would for the Jest example.
Angular projects (the most common scenario in which you would be using Jasmine as a testing framework) include a tsconfig.spec.json file that extends the tsconfig.json base configuration when unit tests are being executed. Modify this file to extend any paths mapping you may have at the base level.
For example, if your tsconfig.json file contains the following paths mapping:
"paths": {
"@app/*": ["src/app/*"],
"@env/*": ["src/environments/*"]
},
Then update your tsconfig.spec.json file to include those paths plus any you would like to use for the unit tests:
"paths": {
"@app/*": ["src/app/*"],
"@env/*": ["src/environments/*"],
"@test/*": ["test/*"],
"@capacitor/*": ["__mocks__/@capacitor/*"]
}
Now when the unit tests are compiled, import { Storage } from '@capacitor/storage'; will use the stub file under __mocks__/@capacitor rather than the real one in node_modules.
Note: the paths object is replaced entirely rather than being merged, so if you have any paths defined at in tsconfig.json they must also be included in tsconfig.spec.json.
Mocking the Stubs
With the manual mocks in place, the tests can now be written to mock and spy on the method calls in all of the usual ways.
Jest
it("gets the first and last name", async () => {
Storage.get = jest.fn().mockImplementation(
async (data: { key: string }): Promise<{ value: string }> => {
return data.key === "firstName"
? { value: "Jimmy" }
: data.key === "lastName"
? { value: "Simms" }
: { value: "unknown" };
}
);
const w = mount(Home);
await flushPromises();
expect(w.vm.firstName).toEqual("Jimmy");
expect(w.vm.lastName).toEqual("Simms");
});
it("clears the storage", () => {
const button = wrapper.findComponent('[data-testid="clear"]');
Storage.clear = jest.fn().mockResolvedValue(undefined);
button.trigger("click");
expect(Storage.clear).toHaveBeenCalledTimes(1);
});
Jasmine
it("gets the first and last name", async () => {
spyOn(Storage, 'get');
(Storage.get as any)
.withArgs({ key: 'firstName' })
.and.returnValue(Promise.resolve({ value: 'Jason' }));
(Storage.get as any)
.withArgs({ key: 'lastName' })
.and.returnValue(Promise.resolve({ value: 'Jones' }));
fixture.detectChanges();
await fixture.whenRenderingDone();
expect(component.firstName).toEqual('Jason');
expect(component.lastName).toEqual('Jones');
});
it('clears the storage', () => {
spyOn(Storage, 'clear');
click(clear.nativeElement);
fixture.detectChanges();
expect(Storage.clear).toHaveBeenCalledTimes(1);
});