describe("[[Call]] trap normal behavior", () => {
  test("forwarding when not defined in handler", () => {
    let p = new Proxy(() => 5, { apply: null });
    expect(p()).toBe(5);
    p = new Proxy(() => 5, { apply: undefined });
    expect(p()).toBe(5);
    p = new Proxy(() => 5, {});
    expect(p()).toBe(5);
  });

  test("correct arguments supplied to trap", () => {
    const f = (a, b) => a + b;
    const handler = {
      apply(target, this_, arguments) {
        expect(target).toBe(f);
        expect(this_).toBe(handler);
        if (arguments[2]) return arguments[0] * arguments[1];
        return f(...arguments);
      },
    };
    p = new Proxy(f, handler);

    expect(p(2, 4)).toBe(6);
    expect(p(2, 4, true)).toBe(8);
  });
});

describe("[[Call]] invariants", () => {
  test("target must have a [[Call]] slot", () => {
    [{}, [], new Proxy({}, {})].forEach(item => {
      expect(() => {
        new Proxy(item, {})();
      }).toThrowWithMessage(TypeError, "[object ProxyObject] is not a function");
    });
  });
});