Im having issue with gitlab plugin test connection on jenkins. it gives error when I hit the "test connection" button with the given values. GitLab user is maintainer and has full access on it. GitLab API token belongs to this user.
unfortunately it seems no way to track this error. I checked the logs files in jenkins machine as well.
GitLab Plugin Version is -> 1.5.27
you may see screenshot of the page here
alternative link: