defining-mock-services.md

Defining Mock Services

The MockServiceProxy class is a concrete implementation of IServiceProxy that supports defining mock services, and exposes a method for each HTTP CRUD operation:

MockServiceProxy Method	HTTP Verb
addCreateOperation	POST
addReadOperation	GET
addPatchOperation	PATCH
addUpdateOperation	PUT
addDeleteOperation	DELETE

For mock services, you define a URI, and optionally, a function to handle requests:

serviceProxy.addReadOperation('/my-bank-balance/', () => 10000000000000000);

serviceProxy.addCreateOperation('/products/product/', (uriParameters, requestBody) => {
  mockProducts.push({ id: mockProducts.length, requestBody.price, requestBody.name });
});

serviceProxy.addPatchOperation('/high-score/', (uriParameters, requestBody) => {
  highScore = requestBody;
});

serviceProxy.addUpdateOperation('/high-score/', (uriParameters, requestBody) => {
  highScore = requestBody;
});

serviceProxy.addDeleteOperation('/foo-bar/');

URI Parameters

Mock service operations support simple URI parameters:

serviceProxy.addUpdateOperation('/products/product/{productId}/price/', (urlParameters, requestBody) => {
  mockProducts[urlParameters.productId].price = requestBody;
});

Regex URI

For more complex URI matching, using a regex is possible:

serviceProxy.addUpdateOperation(/\/products\/product\/(\d+)\/price\//, (regexMatches, requestBody) => {
  mockProducts[regexMatches[1]].price = requestBody;
});

Global Parameters

Many times, it is necessary to modify the behavior on demand of a mock service operation, such as when writing tests. The service proxy allows passing in parameters that service operations can access:

serviceProxy.addGlobalParameter('bank-balance', 20);

serviceProxy.addReadOperation('/my-bank-balance/', (uriParameters, requestBody, globalParams) => {
  return globalParams['bank-balance'];
});

const bankBalance = await serviceProxy.readViaService('/my-bank-balance/'); // 20

serviceProxy.addGlobalParameter('make-product-create-fail', true);

serviceProxy.addCreateOperation('/products/product/', (uriParameters, requestBody, globalParams) => {
  if (globalParams['make-product-create-fail'] === true) {
    throw new Error('Product create failed!');
  } else {
    mockProducts.push({ id: mockProducts.length, requestBody.price, requestBody.name });
  }
});

await serviceProxy.createViaService('/my-bank-balance/', { price: 500, name: 'Bicycle' }); // Product create failed!

HTTP Status Codes

HTTP status codes get logged when a mock service is called. By default, mock service HTTP status codes are determined as follows:

• When the service operation's function returns something, the status code will be 200
• If a service operation has only a URI and no function defined, the status code will be 204
• If an attempt is made to call a service operation that doesn't exist, the resulting status code will be 404
• If an error is thrown within the service operation's function, the status code will be 500

It is also possible to define custom HTTP response codes within the service operation function:

serviceProxy.addReadOperation('/my-bank-balance/', () => {
  if (isLoggedIn) {
    return 10000000000000;
  } else {
    return {
      status: 401,
      responseBody: 'Please login'
    };
  }
});

HTTP Headers

Mock services can also return HTTP headers, which get logged when the mock service is called:

serviceProxy.addReadOperation('/foo/', () => {
  return {
    status: 200,
    responseBody: 'Bar',
    headers: { foo: 'baz', bar: 'saz' }
  };
});

Logged Calls

The mock service proxy logs every call, which is often useful for test assertions:

const bankBalance = await serviceProxy.readViaService('/my-bank-balance/');

expect(serviceProxy.loggedCalls[0].response.status).toBe(200);
expect(serviceProxy.loggedCalls[0].response.responseBody).toBe(10000000000000000);

await serviceProxy.createViaService('/products/product/', { price: 500, name: 'Bicycle' });

expect(serviceProxy.loggedCalls[1].requestBody.price).toBe(500);
expect(serviceProxy.loggedCalls[1].requestBody.name).toBe('Bicycle');

const bar = await serviceProxy.readViaService('/foo/');

expect(serviceProxy.loggedCalls[2].headers.foo).toBe('baz');
expect(serviceProxy.loggedCalls[2].headers.bar).toBe('saz');