public void FindByFirstKey_SouldFindAllValuesAddedByGivenFirstKey()
{
// arrange
var dic = new BiDictionary <int, string, string>();
// act
dic.Add(2, "two", "second");
dic.Add(2, "three", "third");
dic.Add(3, "four", "fourth");
var actual = dic.FindAllByFirstKey(2);
// assert
Assert.AreEqual(2, actual.Count);
}