earnings/CustomIncrementer.spec.js

const newScene = require("./Domain/newScene")
const newUseCase = require("./Domain/newUseCase")

let useCase;
let scene;

function runApplication() {
  scene = newScene({
    display: jest.fn()
  })
  const rate = 10
  useCase = newUseCase(scene, {
    rate
  })
}

beforeEach(runApplication)

test("should be 0 when render first time", () => {
  expect(scene.display).toHaveBeenCalledWith({
    earning: 0
  })
})
test("should increment by 1 when executes", () => {
  useCase.execute()
  expect(scene.display).toHaveBeenCalledWith({
    earning: 10
  })
  useCase.execute()
  expect(scene.display).toHaveBeenCalledWith({
    earning: 20
  })
})