react-hook-form/src/__tests__/utils/isString.test.ts

import isString from '../../utils/isString';

describe('isString', () => {
  it('should return true when value is a string', () => {
    expect(isString('')).toBeTruthy();
    expect(isString('foobar')).toBeTruthy();
  });

  it('should return false when value is not a string', () => {
    expect(isString(null)).toBeFalsy();
    expect(isString(undefined)).toBeFalsy();
    expect(isString(-1)).toBeFalsy();
    expect(isString(0)).toBeFalsy();
    expect(isString(1)).toBeFalsy();
    expect(isString({})).toBeFalsy();
    expect(isString([])).toBeFalsy();
    expect(isString(new String('test'))).toBeFalsy();
    expect(isString(() => null)).toBeFalsy();
  });
});