Test Runner window search is slow in projects with a lot of tests

Steps to reproduce:

1. Create a project with the TestFramework package
2.  Use a script to generate a few thousands of tests that perform an expensive operation as part of the constructor
3.  Open Test Runner window and try to search through the tests

Actual results: 
There is a short hang after every keystroke. There is a measurable delay in method execution as the Test Runner window is reloaded after each input. This can be observed more accurately using a profiling tool like Superluminal.

Expected results: 
No perceived delay / search is performed once the user finishes input sequence

Reproducible with versions: 
6000.0 (latest), 6000.2 (latest), 6000.3 (latest), 6000.4 (latest)

Not reproducible with versions: 
N/A

Can’t test with versions: 
N/A

Tested on (OS): 
Windows