Cannot connect to Oracle database server through SQL Developer but Test works OK
When you connect from the connection properties dialog, two things will happen in the UI:




the connection icon gets a 'connected' overlay
you get a SQL Worksheet***


If your connection is not successful, you'll get an error message, with the text shown at the bottom of the connection properties window.



***For #2 above, this is conditional on the following preference being enabled, which the default is TRUE.

'Open a Worksheet on connect'