fake.yieldsAsync([value1, ..., valueN]);

Similar to fake.yields, fake.yieldsAsync also returns a function that when invoked, expects its last argument to be a callback, and invokes that callback with the same previously given values.

However, the returned function invokes that callback asynchronously rather than immediately, i.e. in the next event loop.

import tap from "tap";
import * as sinon from "sinon";
import fs from "fs";

tap.test("fake.yieldsAsync", (t) => {
  const fake = sinon.fake.yieldsAsync(null, "file content");
  const anotherFake = sinon.fake();

  sinon.replace(fs, "readFile", fake);

  fs.readFile("somefile", (err, data) => {
    // called with fake values given to yields as arguments
    t.equal(err, null, "callback receives null error");

    t.equal(data, "file content", "callback receives file content");

    // since yields is asynchronous, anotherFake is called first
    t.ok(anotherFake.called, "anotherFake was called before callback");

    sinon.restore();
    t.end();
  });

  anotherFake();
});

tap.test(
  "fake.yieldsAsync throws when last argument is not a function",
  (t) => {
    const fake = sinon.fake.yieldsAsync("error", "data");

    t.throws(
      () => fake("not a callback"),
      /Expected last argument to be a function/,
      "throws TypeError when last argument is not a function"
    );

    t.end();
  }
);