stub.addBehavior(name, fn)

Add a custom behavior. The name will be available as a function on stubs, and the chaining mechanism will be set up for you (e.g. no need to return anything from your function, its return value will be ignored). The fn will be passed the fake instance as its first argument, and then the user's arguments.

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

tap.test("stub.addBehavior - custom behavior", (t) => {
  const name = "returnsNum";

  function fn(fake, n) {
    fake.returns(n);
  }

  sinon.addBehavior("returnsNum", fn);

  const stub = sinon.stub().returnsNum(42);

  const result = stub();

  t.equal(result, 42, "custom behavior returns 42");

  t.end();
});