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Observing changes in the MockFileSystem #805
Description
Activity
This is the same as #168 which has gone stale.
As mentioned over there I generally like the idea and would accept a contribution here unless it's getting overly complex.
The neat thing about this kind of approach is that it makes testing certain scenarios easier. For example:
var fileSystem = new MockFileSystem(new MockFileSystemOptions { EnableEvents = true }); // Make everything read-only with one subscription using (fileSystem.Events.Subscribe(args => { if (args.Phase == OperationPhase.Before && (args.Operation == FileOperation.Write || args.Operation == FileOperation.Delete || args.Operation == FileOperation.Create)) { args.SetResponse(new OperationResponse { Exception = new UnauthorizedAccessException("File system is read-only") }); } })) { // This will throw UnauthorizedAccessException fileSystem.File.WriteAllText(@"C:\test.txt", "data"); }
Or generic logging, etc.
var fs = new MockFileSystem(new MockFileSystemOptions { EnableEvents = true }); var log = new List<string>(); using (fs.Events.Subscribe(args => { if (args.Phase == OperationPhase.After) log.Add($"{args.Operation} on {args.Path}"); })) { // Your test code here MyService.ProcessFiles(fs); // Now you can assert on what actually happened Assert.That(log, Contains.Item("Delete on C:\\temp\\cache.tmp")); }
// Simulate disk full on the third write var writeCount = 0; using (fs.Events.Subscribe(FileOperation.Write, args => { if (++writeCount >= 3 && args.Phase == OperationPhase.Before) { args.SetResponse(new OperationResponse { Exception = new IOException("Disk full") }); } })) { // Test your retry logic, error handling, etc. }
// Prevent deletion of important files using (fs.Events.Subscribe(FileOperation.Delete, args => { if (args.Phase == OperationPhase.Before && args.Path.EndsWith(".config")) { args.SetResponse(new OperationResponse { Exception = new UnauthorizedAccessException("Config files are protected") }); } })) { // Deletion is prevented }
The actual syntax to add events is pretty minimal. For example:
return mockFileDataAccessor.Events.WithEvents(fullPath, FileOperation.Read, ResourceType.File, () => { // ... existing code return ReadAllTextInternal(path, encoding); });
Describe the solution you'd like
I'd like to be able to observe common/interesting events (from a testing perspective) that happen into a
MockFileSystem.Why? I'm creating a cache service that uses an
IFileSystemand I need to test that a file is only written once.Describe alternatives you've considered
I've tried to implement my own
MockFileSystemusing System.Reactive, but the work is a bit overwhelming.