No Lock

This dialog box is displayed if multiple instances of SQL Developer are running on the system and if you attempt to open a unit test object, such as a test or suite, when that object is already open in another instance of SQL Developer. Thus, the current instance of SQL Developer is unable to get a lock on that object at this time.

Either use the other instance of SQL Developer to view or modify the object, or close the object in the other instance of SQL Developer and then open the object in this instance.