Method 1 Tests:

[TestClass]
    public class GetQueuePosition_Should
    {
        [TestMethod]
        public void ReturnCorrectQueuePosition()
        {
            // Arrange
            var options = TestUtilities.GetOptions(nameof(ReturnCorrectQueuePosition));

            var testBook = new Book
            {
                Title = "Test",
                Author = "Test",
                Subject = "Test",
                Pages = 23,
                Year = 23,
                Country = "Test",
                Language = "Test",
                Link = "Test",
            };
            var testUser = new User
            {
                Email = "test@test.test",
                UserName = "Test"
            };
            var testUser1 = new User
            {
                Email = "test@test.test",
                UserName = "Test12"
            };

            // Act, Assert
            using (var assertContext = new LibraryDbContext(options))
            {
                var sut = new ReservationsServices(assertContext);

                var reservation = sut.CreateReservation(testUser, testBook).GetAwaiter().GetResult();
                var reservation1 = sut.CreateReservation(testUser1, testBook).GetAwaiter().GetResult();

                var expected = 2;
                var actual = sut.GetQueuePositionAsync(testUser1, testBook).GetAwaiter().GetResult();
                Assert.AreEqual(expected, actual);
            }
        }
    }

Method 2 Tests:
    [TestClass]
    public class IsUserFirstToCheckOut_Should
    {
        [TestMethod]
        public void ReturnFalseIfTheBookIsNotReservedByTheUser()
        {
            // Arrange
            var options = TestUtilities.GetOptions(nameof(ReturnFalseIfTheBookIsNotReservedByTheUser));

            var testBook = new Book
            {
                ID = 1,
                Title = "Test",
                Author = "Test",
                Subject = "Test",
                Pages = 23,
                Year = 23,
                Country = "Test",
                Language = "Test",
                Link = "Test",
            };
            var testUser = new User
            {
                Id = "1",
                Email = "test@test.test",
                UserName = "Test"
            };

            // Act, Assert
            using (var assertContext = new LibraryDbContext(options))
            {
                var sut = new ReservationsServices(assertContext);

                var expected = false;
                var actual = sut.IsUserFirstToCheckOutAsync(testUser.Id, testBook.ID).GetAwaiter().GetResult();

                Assert.AreEqual(expected, actual);
            }
        }

        [TestMethod]
        public void ReturnFalseIfTheUserIsNotFirstToCheckOut()
        {
            // Arrange
            var options = TestUtilities.GetOptions(nameof(ReturnFalseIfTheUserIsNotFirstToCheckOut));

            var testBook = new Book
            {
                ID = 1,
                Title = "Test",
                Author = "Test",
                Subject = "Test",
                Pages = 23,
                Year = 23,
                Country = "Test",
                Language = "Test",
                Link = "Test",
            };
            var testUser = new User
            {
                Id = "1",
                Email = "test@test.test",
                UserName = "Test"
            };
            var testUser1 = new User
            {
                Id = "2",
                Email = "test@test.test",
                UserName = "Test12"
            };

            // Act, Assert
            using (var assertContext = new LibraryDbContext(options))
            {
                var sut = new ReservationsServices(assertContext);

                var reservation = sut.CreateReservation(testUser, testBook).GetAwaiter().GetResult();
                var reservation1 = sut.CreateReservation(testUser1, testBook).GetAwaiter().GetResult();

                var expected = false;
                var actual = sut.IsUserFirstToCheckOutAsync(testUser1.Id, testBook.ID).GetAwaiter().GetResult();

                Assert.AreEqual(expected, actual);
            }
        }

        [TestMethod]
        public void ReturnTrueIfTheUserIsFirstToCheckOutTheBook()
        {
            // Arrange
            var options = TestUtilities.GetOptions(nameof(ReturnFalseIfTheUserIsNotFirstToCheckOut));

            var testBook = new Book
            {
                ID = 1,
                Title = "Test",
                Author = "Test",
                Subject = "Test",
                Pages = 23,
                Year = 23,
                Country = "Test",
                Language = "Test",
                Link = "Test",
            };
            var testUser = new User
            {
                Id = "1",
                Email = "test@test.test",
                UserName = "Test"
            };
            var testUser1 = new User
            {
                Id = "2",
                Email = "test@test.test",
                UserName = "Test12"
            };

            // Act, Assert
            using (var assertContext = new LibraryDbContext(options))
            {
                var sut = new ReservationsServices(assertContext);

                var reservation = sut.CreateReservation(testUser, testBook).GetAwaiter().GetResult();
                var reservation1 = sut.CreateReservation(testUser1, testBook).GetAwaiter().GetResult();

                var expected = true;
                var actual = sut.IsUserFirstToCheckOutAsync(testUser.Id, testBook.ID).GetAwaiter().GetResult();

                Assert.AreEqual(expected, actual);
            }
        }
    }