Sample test (not full, only to show code)

Chat.spec.tsx

mport 'jest'

import { clock } from 'testing/setupFakeTimers'
import { TestController as Ctrl } from 'testing/testController'

import React from 'react'
import Renderer, { act } from 'react-test-renderer'

beforeEach(() => {
  // simplifyed code
  Ctrl.setup()
  clock.tick(200)
  Ctrl.simulateApplicationStart()
  clock.tick(200)
})

afterEach(() => {
  // wait application to stop any activity (because LazyLoader can't cancel its promises)
  clock.runAll()
  Ctrl.reset()
  jest.clearAllMocks()
  clock.reset()
})

it('renders empty screen until chat will be loaded', () => {
  const r = Renderer.create(<ChatScreen screenId="screen0" chatId="ch0" />)
  expect(r.toJSON()).toMatchSnapshot()

  act(() => {
    Ctrl.app.model.chats.addFromApi({
      id: 'ch0',
      lastSeen: '',
      lastSeenMessageId: '',
      peerId: 'u1',
      type: 'personal',
      unreadCount: 0,
    })
  })
  expect(r.toJSON()).toMatchSnapshot()

  act(() => {
    Ctrl.app.model.users.addFromApi(UserSysType.Short, {
      about: '',
      age: 30,
      authType: ['local'],
      avatarUrl: 'https://avatars/u1',
      chatAllowed: true,
      displayName: 'User 1',
      id: 'u1',
      sex: 'm',
      subscribedCategories: [],
    })
  })
  expect(r.toJSON()).toMatchSnapshot()

  r.unmount()
})