public void Corpus_GetLetter_ExistsAndMathcingCoreLetter()
{
// Arrange
var corpus = new Corpus();
corpus.Letters = new List <Letter>()
{
new Letter("a")
};
// Act
var letter = corpus.GetLetter("a");
// Assert
Assert.That(letter, Is.Not.Null);
Assert.That(letter.CoreLetter, Is.EqualTo("a"));
}