what is the best way to test a journey in case the entry source is SALESFORCE DATA? i tried to create fake leads based on the filtering criteria i did choose in my entry source, then i did validate and activate the journey, but it didn't work and none of those leads entered it. #
It would be great if you can post your Entry criteria rules for this Journey.
With entry source being Salesforce Data, the best way to test is exactly what you have tried - by using the connected Sales Cloud to inject (test) Contacts/Leads to your Journey.
In your scenario if the Lead did not enter to the Journey, then it's likely the configuration of the Entry Event isn't done properly or the manual updates done on Sales Cloud side were not matching the criteria.
It's also possible that there is an issue with your MC Connect, best make sure this is working properly before going any further. Check on Sales Cloud side if the token is current and valid and make sure the integration user has all necessary permissions.
To troubleshoot Salesforce Data Entry, you can Initiate Logging on Sales Cloud side before you try to update Contacts/Leads for injecting to Journey. If there is an issue with tokens you can clear invalid tokens.