Hash Code

var hashes = new Dictionary<int, string>();
var collisions = new List<string>();

for (int i = 0; ; ++i)
{
    string st = i.ToString();
    int hash = st.GetHashCode();

    if (hashes.TryGetValue( hash, out string collision ))
    {
        // On .Net 4.6 we find "699391" and "1241308".
        collisions.Add( collision );
        collisions.Add( st );
        break;
    }
    else
        hashes.Add( hash, st );
}
Debug.Assert( collisions[0] != collisions[1], "Check we have produced two different strings" );
Debug.Assert( collisions[0].GetHashCode() == collisions[1].GetHashCode(), "Prove we have different strings producing the same hashcode" );

var newDictionary = new Dictionary<string, string>();
newDictionary.Add( collisions[0], "abc" );
newDictionary.Add( collisions[1], "def" );

Console.Write( "If we get here without an exception being thrown, it demonstrates a dictionary accepts multiple items with different keys that produce the same hash value." );

Debug.Assert( newDictionary[collisions[0]] == "abc" );
Debug.Assert( newDictionary[collisions[1]] == "def" );