public async Task GetWithIsbnAsync_NullIsbn_Fails()
        {
            //arrange
            var invalidBooks = BookCopyMapTestUtils.GenerateValidBookCopyMapEnumerable();

            _access.WithGetByIsbnAsyncResult(invalidBooks);

            _sut = new BookCopyRepository(_access.Object, _mapper.Object);

            //act
            var result = await _sut.GetByIsbnAsync(null);

            //assert
            _access.Verify(m => m.GetByIsbnAsync(It.IsAny <string>()), Times.Never);
            Assert.IsNull(result);
        }
        public async Task GetWithIsbnAsync_ValidIsbn_HappyPath()
        {
            //arrange
            var validBooks = BookCopyMapTestUtils.GenerateValidBookCopyMapEnumerable();
            var isbn       = BookTestUtils.GenerateValidBook().Isbn;

            _access.WithGetByIsbnAsyncResult(validBooks);

            _sut = new BookCopyRepository(_access.Object, _mapper.Object);

            //act
            var result = await _sut.GetByIsbnAsync(isbn);

            //assert
            _access.Verify(m => m.GetByIsbnAsync(It.IsAny <string>()), Times.Once);
            Assert.IsNotNull(result);
        }