Reviewed 4 of 4 files at r1.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @chaehni)

go/hidden_path_srv/internal/registration/handler_test.go, line 153 at r1 (raw file):

				context.Background(), mocks.rw)
			handler := registration.NewSegRegHandler(
				registration.NullValidator,

Instead of always using a NullValidator you could also use a mock validator, then you could also test that failing validation triggers the correct action.
For that you would need to modify tools/gomocks, then run make mocks then you can use the mock here: mock_registration.NewMockValidator(ctrl)

go/hidden_path_srv/internal/registration/validator.go, line 104 at r1 (raw file):

// NullValidator validates all input
var NullValidator = nullValidator{}

If it's only used for testing then I would also define it in the test file. I don't think this ever makes sense in non-testing code.

Reviewable status: 1 of 6 files reviewed, 2 unresolved discussions (waiting on @lukedirtwalker)

go/hidden_path_srv/internal/registration/handler_test.go, line 153 at r1 (raw file):

You're right. That makes more sense.

go/hidden_path_srv/internal/registration/validator.go, line 104 at r1 (raw file):

With the mock Validator its no longer needed. I have removed it.

Reviewed 6 of 6 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved