public void TestIEnumeratorT()
{
ImmutableTreeSet <int> .Builder set = ImmutableTreeSet.CreateBuilder <int>();
IEnumerator <int> enumerator = set.GetEnumerator();
Assert.Equal(0, enumerator.Current);
Assert.False(enumerator.MoveNext());
Assert.Equal(0, enumerator.Current);
// Adding an item to the list invalidates it, but Current is still unchecked
CollectionAssert.EnumeratorInvalidated(set, () => set.Add(1));
Assert.Throws <InvalidOperationException>(() => enumerator.MoveNext());
Assert.Throws <InvalidOperationException>(() => enumerator.Reset());
Assert.Equal(0, enumerator.Current);
enumerator = set.GetEnumerator();
Assert.Equal(0, enumerator.Current);
Assert.True(enumerator.MoveNext());
Assert.Equal(1, enumerator.Current);
Assert.False(enumerator.MoveNext());
Assert.Equal(1, enumerator.Current);
enumerator.Reset();
Assert.Equal(0, enumerator.Current);
Assert.True(enumerator.MoveNext());
Assert.Equal(1, enumerator.Current);
enumerator.Reset();
Assert.Equal(0, enumerator.Current);
Assert.True(enumerator.MoveNext());
Assert.Equal(1, enumerator.Current);
Assert.False(enumerator.MoveNext());
Assert.Equal(1, enumerator.Current);
}