Cancellation

The rule

Every async call that can be cancelled is given the token of the request that started it, all the way down to the database. When a caller goes away, the work stops.

Steps

1. Add CancellationToken cancellationToken as the last parameter of any new async method.
2. Pass it to sender.Send(request, cancellationToken), to every repository call, and to every EF Core method (ToListAsync, CountAsync, ExecuteUpdateAsync, SaveChangesAsync).
3. In tests, create a real token and assert it's the one that reached the mock (unit-tests):

using var tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;

// Act
var result = await handler.Handle(command, token);

// Assert
_ = await reviewsRepository.Received(1).UpdateReview(command.Id, command.Stars, command.Text, token);

Don't

• Use CancellationToken.None or default outside tests.
• Leave the token out of one call in a chain. Every hop needs it.
• Make the token optional (= default) on an interface method.

Check

dotnet build
dotnet test