Hey Itay,
When you add the "Test Variant" constraint to the smart list filter, you will only see leads who received/opened during the test.
For example, if you create a filter like "Opened email is 'Email 1'" with the constraint "Test Variant is Subject A", you will only see leads who opened email A during the test.
To show those who only opened as part of the "Winner" send,create a list with these filters:
--- Use all filters ---
Filter one = Opened email1
Filter Two = Not opened email1 (Include the test variant constraint and select email A)
Filter Three = Not opened email1 (Include the test variant constraint and select email b)
This will be everyone who opened email A during the "Winner" send (assuming email A was the winner).
Thanks!
Trevor