public void When_creating_a_new_keyedCollectionEx_with_non_default_comparer()
        {
            var personA = new Person {
                Name = "A", Age = 1
            };
            var personB = new Person {
                Name = "B", Age = 2
            };
            var personC = new Person {
                Name = "C", Age = 3
            };

            var collection = new KeyedCollectionEx <string, Person>(p => p.Name, StringComparer.OrdinalIgnoreCase)
            {
                personA,
                personB
            };

            collection.ShouldNotBeNull();
            collection.Count.ShouldBe(2);
            collection.Contains("A").ShouldBeTrue();
            collection.Contains("a").ShouldBeTrue();
            collection.Contains("B").ShouldBeTrue();
            collection.Contains("b").ShouldBeTrue();
            collection.Contains("C").ShouldBeFalse();
            collection.Contains("c").ShouldBeFalse();

            collection.Contains(personA).ShouldBeTrue();
            collection.Contains(personB).ShouldBeTrue();
            collection.Contains(personC).ShouldBeFalse();

            collection.Add(personC);
            collection.Contains("C").ShouldBeTrue();
            collection.Contains("c").ShouldBeTrue();
            collection.Contains(personC).ShouldBeTrue();

            var dodgyPerson = new Person {
                Name = "A", Age = 666
            };

            Should.Throw <ArgumentException>(() => collection.Add(dodgyPerson)).Message
            .ShouldBe("An item with the same key has already been added.");

            collection["A"].Age.ShouldBe(1);
            collection["B"].Age.ShouldBe(2);
            collection["C"].Age.ShouldBe(3);

            Person somePerson;

            collection.TryGet("A", out somePerson).ShouldBeTrue();
            somePerson.ShouldNotBeNull();
            somePerson.Age.ShouldBe(1);

            collection.TryGet("D", out somePerson).ShouldBeFalse();
            somePerson.ShouldBeNull();
        }
 /// <summary>
 /// Adds the <paramref name="key"/> and <paramref name="value"/> to the <paramref name="keyedCollection"/>
 /// if the <paramref name="key"/> does not already exists and returns the inserted value.
 /// </summary>
 public static TValue GetOrAdd <TKey, TValue>(this KeyedCollectionEx <TKey, TValue> keyedCollection, TKey key, TValue value)
 {
     if (!keyedCollection.TryGet(key, out TValue result))
     {
         keyedCollection.Add(value);
         return(value);
     }
     return(result);
 }
 /// <summary>
 /// Adds the <paramref name="key"/> and the value created by <paramref name="valueCreator"/> to
 /// the <paramref name="keyedCollection"/> if the <paramref name="key"/> does not already exists
 /// and returns the inserted value.
 /// </summary>
 public static TValue GetOrAdd <TKey, TValue>(this KeyedCollectionEx <TKey, TValue> keyedCollection, TKey key, Func <TValue> valueCreator)
 {
     if (!keyedCollection.TryGet(key, out TValue result))
     {
         var value = valueCreator();
         keyedCollection.Add(value);
         result = value;
     }
     return(result);
 }