I can't find any description of the test across the three reports mentioning that that emergency stop button is supposed to be pressed as part of the test. AFAICT the test wasn't even completed when the button was pressed as the purpose of the test was to demonstrate that the emergency core cooling system could run for at least 40 s (INSAG-1 page 17) after closing the turbine emergency stop valve. That valve was closed at 01:23:04 and AZ-5 was pressed at 01:23:40.