.tobeinstanceof(string)在jest测试中的buffer.tostring()上

Question

如何在开玩笑的断言中使用expect(str).toBeInstanceOf(String)，用于使用Buffer#toString()创建的字符串？

或者在这里做正确的事情expect(typeof str).toEqual('string')？

---

详细信息：

使用typeof的测试案例通过：

it('should test a Buffer.toString() - typeof', () => {
  const buf = new Buffer('hello world');
  const str = buf.toString('hex');
  expect(buf).toBeInstanceOf(Buffer);
  expect(typeof str).toEqual('string');
  // expect(str).toBeInstanceOf(String);
});

但是，使用.toBeInstanceOf()的测试案例失败：

it('should test a Buffer.toString()', () => {
  const buf = new Buffer('hello world');
  const str = buf.toString('hex');
  expect(buf).toBeInstanceOf(Buffer);
  // expect(typeof str).toEqual('string');
  expect(str).toBeInstanceOf(String);
});

这是它的嘲笑输出：

 FAIL  ./buffer.jest.js
  ● should test a Buffer.toString()
    expect(value).toBeInstanceOf(constructor)
    Expected value to be an instance of:
      "String"
    Received:
      "68656c6c6f20776f726c64"
    Constructor:
      "String"
      at Object.<anonymous>.it (password.jest.js:11:15)
      at Promise.resolve.then.el (node_modules/p-map/index.js:42:16)
      at process._tickCallback (internal/process/next_tick.js:109:7)

Answer 1

如果您查看了实现的tobeinstance，您会看到instanceof用于检查，但是如您在Mozilla Docs中所示的那样，string primitive与String衍生自Object。

您的第一个变体是检查的正确方法：

expect(typeof str).toEqual('string');