Now with mocking

structural_typing3.ts

import { expect } from 'chai';
import 'mocha';
import { mock, instance, when, anyString, verify } from "ts-mockito";

class HelloEndpoint {
  constructor(private service: HelloService) {}

  async handle(evt: any): Promise<any> {
    const greeting = await this.service.sayHello(evt.queryStringParameters.name);
    return {
      body: greeting
    };
  }
}

// Concrete implementation
class HelloService {

  async sayHello(name: string): Promise<string> {
    throw Error("Not implemented yet")
  }

}

const mockedHelloService: HelloService = mock(HelloService);
const helloService: HelloService = instance(mockedHelloService);

when(mockedHelloService.sayHello(anyString()))
  .thenCall(name => Promise.resolve(`Hello, ${name}!`));

const helloEndpoint = new HelloEndpoint(helloService);

describe("The Hello Endpoint", () => {
  it("Should greet the person", async () => {
    // Call the endpoint.
    const result = await helloEndpoint.handle({
      queryStringParameters: {
        name: "Arthur Putey"
      }
    });

    // Validate that the right data is passed into the service.
    verify(mockedHelloService.sayHello("Arthur Putey")).once();

    // Validate that the right response is returned to the client.
    expect(result.body).to.equal("Hello, Arthur Putey!");
  });
});