如何在 Jest 中模拟局部变量以进行单元测试？

Question

I have two files, file.component.ts containing:

  setTwoNumberDecimal(e) {
    const USER_VAL = parseFloat(e.target.value.replace(/,/g, ''));
    e.target.value = this.getTruncatedValue(USER_VAL, 1);
  }

and my test file file.component.specs.ts containing:

describe('setTwoNumberDecimal()', () => {
  it('tests commas are removed and user value is set', () => {
    const mockEvent = {target: {value: '5.777,'}};
    component.setTwoNumberDecimal(mockEvent);
    expect(component.setTwoNumberDecimal).toHaveBeenCalled();
  });
});

I want to be able to check that, after setTwoNumberDecimal(e) is run:

1. USER_VAL is equal to '5.777' (that is, the comma has been removed); and

2. e.target.value is equal to '5.77' (that is, the last value has been truncated)

The functionality already works for the comma replace and the truncate.

Answer 1

Test that the value is what you expect it to be in your mocked event.

describe('setTwoNumberDecimal()', () => {
  it('Should truncate decimal from value', () => {
    const mockEvent = {target: {value: '5.777,'}};
    expect(mockEvent.target.value).toEqual('5.77');
  });
  it('Should remove commas from value', () => {
    const mockEvent = {target: {value: '1,234,567.89,'}};
    expect(mockEvent.target.value).toEqual('1234567.89');
  });
});