为res.json()方法创建延迟承诺。请在用户单击按钮后解决此问题。
index.tsx：

import React, { useState } from 'react';

export const Test = () => {
  const [isLeaving, setIsLeaving] = useState(false);
  const handler = async () => {
    setIsLeaving(true);
    const response = await fetch('https://api.jikan.moe/v4/anime/1/full');
    const data = await response.json();
    console.log({ data });
    setIsLeaving(false);
  };
  return (
    <div>
      <p>{!isLeaving ? 'hi' : 'bye'}</p>
      <button onClick={handler}>click me</button>
    </div>
  );
};

index.test.tsx：

import { render, screen, waitFor } from '@testing-library/react';
import '@testing-library/jest-dom';
import userEvent from '@testing-library/user-event';
import React from 'react';

import { Test } from './';

describe('Test component test', () => {
  const result = {
    data: {
      id: 1,
      attributes: {
        titles: { en: 'Fullmetal Alchemist' },
        synopsis: 'After losine.',
      },
    },
  };
  let jsonResolve;
  (global as any).fetch = jest.fn(() =>
    Promise.resolve({
      json: () =>
        new Promise((resolve) => {
          jsonResolve = resolve;
        }),
    })
  );
  it('should show "bye" text before showing "hi" text when data fetching is don', async () => {
    const user = userEvent.setup();
    render(<Test />);
    expect(screen.getByText(/hi/i)).toBeInTheDocument();
    await user.click(screen.getByRole('button', { name: /click me/i }));
    expect(screen.getByText(/bye/i)).toBeInTheDocument();
    jsonResolve(result);
    await waitFor(() => {
      expect(screen.getByText(/hi/i)).toBeInTheDocument();
    });
  });
});

试验结果：

PASS  stackoverflow/75861970/index.test.tsx (8.919 s)
  Test component test
    ✓ should show "bye" text before showing "hi" text when data fetching is don (139 ms)

  console.log
    { data: { data: { id: 1, attributes: [Object] } } }

      at stackoverflow/75861970/index.tsx:9:13

-----------|---------|----------|---------|---------|-------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-----------|---------|----------|---------|---------|-------------------
All files  |     100 |      100 |     100 |     100 |                   
 index.tsx |     100 |      100 |     100 |     100 |                   
-----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        9.337 s