function shouldBe(actual, expected) {
    if (actual !== expected)
        throw new Error(`bad value: ${String(actual)}`);
}

function shouldThrow(func, errorMessage) {
    var errorThrown = false;
    var error = null;
    try {
        func();
    } catch (e) {
        errorThrown = true;
        error = e;
    }
    if (!errorThrown)
        throw new Error('not thrown');
    if (String(error) !== errorMessage)
        throw new Error(`bad error: ${String(error)}`);
}

class A {
    *gen()
    {
        yield this;
        yield this;
        return 42;
    }

    static *staticGen()
    {
        yield this;
        yield this;
        return 42;
    }
}
{
    let a = new A();
    let g = a.gen();
    shouldBe(g.next().value, a);
    shouldBe(g.next().value, a);
    shouldBe(g.next().value, 42);
    shouldBe(g.next().done, true);
}
{
    let a = new A();
    shouldThrow(() => {
        let g = new a.gen();
    }, `TypeError: function is not a constructor (evaluating 'new a.gen()')`);
}

{
    let g = A.staticGen();
    shouldBe(g.next().value, A);
    shouldBe(g.next().value, A);
    shouldBe(g.next().value, 42);
    shouldBe(g.next().done, true);
}
{
    shouldThrow(() => {
        let g = new A.staticGen();
    }, `TypeError: function is not a constructor (evaluating 'new A.staticGen()')`);
}