public async Task PurchaseBackgroundAsync()
{
backgroundStoreMock.Setup(x => x.GetBackgroundAsync(It.IsAny <int>()))
.Returns(new ValueTask <Background>(new Background {
Id = 1, Price = 100
}));
backgroundsOwnedRepositoryMock.Setup(x => x.GetAsync(It.IsAny <long>(), It.IsAny <int>()))
.Returns(new ValueTask <BackgroundsOwned>());
await backgroundService.PurchaseBackgroundAsync(1L, 1);
transactionServiceMock.Verify(
x => x.CreateTransactionAsync(It.IsAny <TransactionRequest>()));
backgroundsOwnedRepositoryMock.Verify(
x => x.AddAsync(It.Is <BackgroundsOwned>(x => x.BackgroundId == 1 && x.UserId == 1L)));
unitOfWorkMock.Verify(x => x.CommitAsync());
}