test(example): add test cases to simple firestore example - @harish-aka-shivi

Author: prescottprue

examples/complete/firestore/src/Todos.test.js

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+import React from 'react'
+import { render, unmountComponentAtNode } from 'react-dom'
+import { act } from 'react-dom/test-utils'
+import { useSelector } from 'react-redux'
+import Todos from './Todos'
+
+jest.mock('react-redux')
+
+describe('Should test the Todos Component', () => {
+  let container = null
+
+  beforeEach(() => {
+    // setup a DOM element as a render target
+    container = document.createElement('div')
+    document.body.appendChild(container)
+  })
+
+  afterEach(() => {
+    // cleanup on exiting
+    unmountComponentAtNode(container)
+    container.remove()
+    container = null
+  })
+
+  it('show empty text when the todo list is empty', () => {
+    const todos = []
+    useSelector.mockReturnValue(todos)
+
+    act(() => {
+      render(<Todos />, container)
+    })
+
+    container.querySelectorAll('li')
+    expect(container.textContent).toBe('Todo list is empty')
+  })
+
+  it('should have one TodoItem in the list', () => {
+    const todos = [
+      {
+        id: 'todoId',
+        name: 'Sample todo',
+        text: 'This is for testing todos'
+      }
+    ]
+
+    useSelector.mockReturnValue(todos)
+    act(() => {
+      render(<Todos />, container)
+    })
+
+    const listItems = container.querySelectorAll('li')
+
+    // this is not a real id, so only text which can be visible is Delete
+    expect(listItems[0].textContent).toBe('Delete')
+  })
+})