When opening the Test Runner window it calls `s_Instance.Close();` if the window has been initialised already. This causes the window to pop out from where ever it is docked, or if something else is docked to it.

Repro steps:

1. Select Window > General > Test Runner
2. Dock Test Runner to any other window or dock another window to Test Runner
3. Select Window > General > Test Runner

Expected result:
Test Runner just gets focused

Actual result:
Test Runner pops out to its own window

I think is was introduced in 5.5.0a1