David T. Lewis uploaded a new version of Chronology-Tests to project The Trunk:
http://source.squeak.org/trunk/Chronology-Tests-dtl.18.mcz

==================== Summary ====================

Name: Chronology-Tests-dtl.18
Author: dtl
Time: 27 January 2019, 1:21:59.414215 pm
UUID: 5411396e-c5fc-4517-97ef-5cf9e7aa5dea
Ancestors: Chronology-Tests-pre.17

Do not use #makeUTC in DateAndTimeTest>>testGetSeconds because it modifies magnitude.

=============== Diff against Chronology-Tests-pre.17 ===============

Item was changed:
  ----- Method: DateAndTimeTest>>testGetSeconds (in category 'Tests') -----
  testGetSeconds
  	"Verify that getSeconds represents whole seconds in the local time zone. For
  	a given instance of DateAndTime, changing the time zone offset changes the
  	local representation, but does not affect magnitude (time since a defiined
  	epoch). Therefore, if time zone offset changes, the asSeconds value should
  	not change, and the getSeconds value should change to reflect local timezone." 
  
  	| dt s1 id stSeconds seconds1 seconds2 |
  	s1 :=  '2019-01-12T10:07:05.18743-05:00'.
  	dt := s1 asDateAndTime.
  	self assert: 18000 seconds negated equals: dt offset.
  	seconds1 := dt getSeconds.
  	self assert: 36425 equals: seconds1.
  	id := dt identityHash.
  	stSeconds := dt asSeconds.
+ 	dt localOffsetSeconds: 0. "make the receiver's timezone GMT, do not change magnitude"
- 	dt makeUTC. "make the receiver's timezone GMT, do not change magnitude"
  	self assert: id equals: dt identityHash. "same object, not a copy"
  	self assert: '2019-01-12T15:07:05.18743+00:00' equals: dt asString.
  	self assert: stSeconds equals: dt asSeconds. "magnitude unchanged"
  	self assert: '2019-01-12T10:07:05.18743-05:00' asDateAndTime equals: dt. "still equal"
  	seconds2 := dt getSeconds.
  	self deny: seconds1 equals: seconds2.
  	self assert: 54425 equals: seconds2.
  
  !