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)}`);
}

function *gen() {
}
var g = gen();

shouldThrow(() => {
    g.next.call({});
}, `TypeError: |this| should be a generator`);


shouldThrow(() => {
    g.throw.call({});
}, `TypeError: |this| should be a generator`);

shouldThrow(() => {
    g.return.call({});
}, `TypeError: |this| should be a generator`);