public void BookCalculatesAnAverageGrades()
{
//arrange my data
var book = new InMemoryBook("");
book.AddGrade(89.1);
book.AddGrade(90.5);
book.AddGrade(77.3);
//act on the behaviours
var result = book.GetStatisitcs();
//Assert
Assert.Equal(85.6, result.Average, 1);
Assert.Equal(90.5, result.High, 1);
Assert.Equal(77.3, result.Low, 1);
//SYMBOLS NOW
Assert.Equal('B', result.Letter);
}