sinon - spy on toString method

问题

In my file, I have something like this:

if(somevar.toString().length == 2) ....

How can I spy on toString from my test file? I know how to spy on things like parseInt with:

let spy = sinon.spy(global, 'parseInt')

But that doesn't work with toString since it's called on the value, I tried spying on Object and Object.prototype, but that doesn't work either.

回答1:

You can't call sinon.spy or sinon.stub on a method of primitive value like:

sinon.spy(1, 'toString'). This is wrong.

You should call them on the Class.prototype of primitive value. Here is the unit test solution:

index.ts:

export function main(somevar: number) {
  if (somevar.toString(2).length == 2) {
    console.log("haha");
  }
}

index.spec.ts:

import { main } from "./";
import sinon from "sinon";
import { expect } from "chai";

describe("49866123", () => {
  afterEach(() => {
    sinon.restore();
  });
  it("should log 'haha'", () => {
    const a = 1;
    const logSpy = sinon.spy(console, "log");
    const toStringSpy = sinon.stub(Number.prototype, "toString").returns("aa");
    main(a);
    expect(toStringSpy.calledWith(2)).to.be.true;
    expect(logSpy.calledWith("haha")).to.be.true;
  });
  it("should do nothing", () => {
    const a = 1;
    const logSpy = sinon.spy(console, "log");
    const toStringSpy = sinon.stub(Number.prototype, "toString").returns("a");
    main(a);
    expect(toStringSpy.calledWith(2)).to.be.true;
    expect(logSpy.notCalled).to.be.true;
  });
});

Unit test result with 100% coverage:

  49866123
haha
    ✓ should log 'haha'
    ✓ should do nothing


  2 passing (28ms)

---------------|----------|----------|----------|----------|-------------------|
File           |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
---------------|----------|----------|----------|----------|-------------------|
All files      |      100 |      100 |      100 |      100 |                   |
 index.spec.ts |      100 |      100 |      100 |      100 |                   |
 index.ts      |      100 |      100 |      100 |      100 |                   |
---------------|----------|----------|----------|----------|-------------------|

Source code: https://github.com/mrdulin/mocha-chai-sinon-codelab/tree/master/src/stackoverflow/49866123

来源：https://stackoverflow.com/questions/49866123/sinon-spy-on-tostring-method