expo install jest-expo jest
yarn add --dev ts-node

...
"scripts": {
    "test": "jest",
...

import { Config } from '@jest/types';

// By default, all files inside `node_modules` are not transformed. But some 3rd party
// modules are published as untranspiled, Jest will not understand the code in these modules.
// To overcome this, exclude these modules in the ignore pattern.
const untranspiledModulePatterns = [
  '(jest-)?react-native',
  '@react-native-community',
  'expo(nent)?',
  '@expo(nent)?/.*',
  'react-navigation',
  '@react-navigation/.*',
  '@unimodules/.*',
  'unimodules',
  'sentry-expo',
  'native-base',
  'react-native-svg',
  '@react-native',
  'react-native',
];

const config: Config.InitialOptions = {
  preset: 'jest-expo',
  transformIgnorePatterns: [`node_modules/(?!${untranspiledModulePatterns.join('|')})`],
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx'],
};

export default config;

import { StatusBar } from 'expo-status-bar';
import { StyleSheet, Text, View } from 'react-native';

export default function App() {
  return (
    <View style={styles.container}>
      <Text>Open up App.tsx to start working on your app!</Text>
      <StatusBar style="auto" />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#fff',
    alignItems: 'center',
    justifyContent: 'center',
  },
});

import React from 'react';
import renderer from 'react-test-renderer';

import App from './App';

describe('<App />', () => {
  it('has 1 child', () => {
    const tree = renderer.create(<App />).toJSON();
    expect(tree.children.length).toBe(1);
  });
});