public void InMemoryBook_CalculatesAnAvverageGrade()
{
//arrange переменные
var book = new InMemoryBook("");
book.AddObjectGrade("A");
book.AddObjectGrade("B");
book.AddObjectGrade("C");
//act вычисления
var result = book.GetStatistics();
//assert утверждение
Assert.Equal(85.6, result.Average, 1);
Assert.Equal(90.5, result.High, 1);
Assert.Equal(77.3, result.Low, 1);
Assert.Equal('B', result.Letter);
}