public void Test1()
{
InMemoryBook book = new InMemoryBook("");
book.AddGrade(89.1);
book.AddGrade(90.5);
book.AddGrade(77.3);
var result = book.GetStat();
Assert.Equal(85.6, result.Average, 1);
Assert.Equal(90.5, result.High);
Assert.Equal(77.3, result.Low);
}