How to use TESTTIME function?

From the TESTTIME inline help

Sets a time to be used with the channel to test logical conditions.

my expectation is that

 exten=>test,1,Answer() 
  same=>n,Set(TESTTIME(2019/09/28,10:00:00)=)
  same=>n,ExecIfTime(09:59-10:01,*,*,*?Playback(hello))

would set “time now” to 2019-09-28 10:00:00, so ExecIf will play hello no matter when this test is called. Any idea why it doesn’t ?

Maybe TESTTIME is kind of dead code? I am using Asterisk certified/13.21-cert3.

Looking at the code, it looks to me as though the documentation is wrong and it should be:

same=>n,Set(TESTTIME()=2019/09/28 10:00:00)