Unit Testing Entities

When we unit test our entities, ideally we would isolate them from the components that use them. What we're testing are the actions and how they update the associated entities.

Since actions are defined outside the entity object, we can easily invoke actions in our tests, then use the entity's get method to inspect its current value.

We can also use the init method to reset the entity to its initial value before each test case.

Here is an example Jest unit test:

counter.test.js

import { counter, increment } from './counter'

describe('counter', () => {
  beforeEach(() => {
    counter.init()  // 👈 Reset value
  })

  describe('increment', () => {
    it('increases the value of the counter', () => {
      //   👇 Invoke action
      increment(1)
      expect(counter.get()).toBe(1)
      //              👆 Inspect value
    })
  })

  // . . .
})

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