public void GetTotalTurnover_NegativeInts_ReturnsProperValue() { TransactionLibrary library = new TransactionLibrary(); List <Transaction> transactions = new List <Transaction>(); transactions.Add(new Transaction() { Id = 1, ProductHistory = new List <ProductHistory>() { new ProductHistory() { Price = -1 }, new ProductHistory() { Price = -3 } } }); transactions.Add(new Transaction() { Id = 2, ProductHistory = new List <ProductHistory>() { new ProductHistory() { Price = -2.50 } } }); var result = library.GetTotalTurnover(new EnumerableQuery <Transaction>(transactions)); Assert.IsTrue(result <-6.49 && result> -6.51); }