public void EitherTestAssignLeft()
{
var item = new T1();
Either <T1, T2> either = new T2();
either.Set(item);
Assert.IsTrue(either.IsLeft);
Assert.IsFalse(either.IsRight);
Assert.AreEqual(item, either.GetLeft());
Assert.ThrowsException <InvalidCastException>(() => either.GetRight());
}