public void CalculateFrequency_Returns_Letter_Counts()
{
// Arrange
string input = "abba";
Dictionary <char, int> inputFrequency = new Dictionary <char, int>();
inputFrequency.Add('a', 2);
inputFrequency.Add('b', 2);
// Act
Dictionary <char, int> frequency = AnagramChecker.CalculateFrequency(input);
// Assert
Assert.AreEqual(inputFrequency, frequency);
}