public void TestTryGetKey()
{
ImmutableSortedTreeDictionary <int, int> .Builder dictionary = ImmutableSortedTreeDictionary.CreateBuilder <int, int>();
Assert.False(dictionary.TryGetKey(0, out var key));
Assert.Equal(0, key);
dictionary.Add(1, 2);
Assert.True(dictionary.TryGetKey(1, out key));
Assert.Equal(1, key);
}