Steps to reproduce:
1. Open the project
2. Go to "Editor Tests" window
3. Find "SimpleInterfaceTest" under "UndoStackTests" dropdown
4. Right click and select "Open in editor" (should be opened with MonoDevelop)
5. Put a breakpoint on line 154 "ISimpleInterface d = new Derived() as ISimpleInterface;"
6. In MonoDevelop press Run->Start debugging
7. In Unity run the "SimpleInterfaceTest"
8. In MonoDevelop, press "Step Over" two times so that the debugger would be evaluating line 156 "Assert.IsTrue( string.Compare(d.val, "1234" + ".derived.base",true, System.Globalization.CultureInfo.InvariantCulture)==0);"
9. Notice how the evaluation times out.

Note: running the test without debugger finishes it successfully.

Reproduced on: 5.4.4f1, 5.5.0p3