I had recently upgraded my Eclipse IDE to V36 from V33. The Eclipse Workspace pointed to two different orgs:

• Developer Edition
• Sandbox for a client’s PROD org

When I ran a Test Configuration for the Developer Edition, the user debug logs appeared in the Apex Test Results pane. But, for the sandbox org, while the tests ran, the user and system debug log panes were empty. Nothing. Zippo. Bupkus. The logs appeared in the Developer Console but not within the Eclipse IDE.

Solution
Eclipse had prompted me to upgrade the project to V36 but I had ignored that message. Silly me. By upgrading the project to the same version as the Eclipse IDE, and rerunning the tests, the debug logs appeared in the Eclipse Apex Test Results pane.