TestClass.spec.tsx

import * as React from 'react';
import * as TestRenderer from 'react-test-renderer';
import TestClass from '../TestClass';
import TestHoc from '../TestHoc';

let renderer: TestRenderer.ReactTestRenderer;

describe("Test Component state change without HOC", () => {
  beforeAll(() => {
    renderer = TestRenderer.create(
      <TestClass />
    );
  });

  it("should have counter element", () => {
    let root = renderer.root;
    const counter = root.findAll(
      (el) => el.props.testID === 'counter' && el.type === 'Text'
    );
    expect(counter).toHaveLength(1);
  });

  it("should count 0 as a default", () => {
    let root = renderer.root;
    const counter = root.findAll(
      (el) => el.props.testID === 'counter' && el.type === 'Text'
    );
    expect(counter[0].children).toEqual(['0']);
  });

  it("should setState the counter to 1", () => {
    let root = renderer.root;
    const instance = root.instance;
    instance.setState({ count: 1 })
    const counter = root.findAll(
      (el) => el.props.testID === 'counter' && el.type === 'Text'
    );
    expect(counter[0].children).toEqual(['1']);
  });
});

describe('Set preps With HOC', () => {

  it("should preset counter to 2", () => {
    const CountFactory = TestHoc({ count: 2 })(TestClass);  
    renderer = TestRenderer.create(
      <CountFactory />
    );

    let root = renderer.root;
    const counter = root.findAll(
      (el) => el.props.testID === 'counter' && el.type === 'Text'
    );
    expect(counter[0].children).toEqual(['2']);
  });
  
});