public void Create()
        {
            IEnumerable <KeyValuePair <string, string> > pairs = new Dictionary <string, string>
            {
                { "a", "b" }
            };
            var keyComparer = StringComparer.OrdinalIgnoreCase;

            var dictionary = ImmutableSegmentedDictionary.Create <string, string>();

            Assert.Equal(0, dictionary.Count);
            Assert.Same(EqualityComparer <string> .Default, dictionary.KeyComparer);

            dictionary = ImmutableSegmentedDictionary.Create <string, string>(keyComparer);
            Assert.Equal(0, dictionary.Count);
            Assert.Same(keyComparer, dictionary.KeyComparer);

            dictionary = ImmutableSegmentedDictionary.CreateRange(pairs);
            Assert.Equal(1, dictionary.Count);
            Assert.Same(EqualityComparer <string> .Default, dictionary.KeyComparer);

            dictionary = ImmutableSegmentedDictionary.CreateRange(keyComparer, pairs);
            Assert.Equal(1, dictionary.Count);
            Assert.Same(keyComparer, dictionary.KeyComparer);
        }