test: add tests for Legend constructor and properties #31695

Job	Run time
Manage labels	0s
Check for required files	-1s
Merge changes from develop branch into this PR	-1s
Update copyright header years	-1s
Remove in-progress label	-7s
Rebase this PR on top of develop branch	-9s
Auto-fix lint errors	-10s
	-29s

Provide feedback