[FSSDK-11236] refactor decision service tests #1068

Job	Run time
crossbrowser_and_umd_unit_tests	6h 0m 13s
lint	1m 14s
unit_tests (16)	1m 31s
unit_tests (18)	1m 25s
unit_tests (20)	1m 24s
unit_tests (22)	1m 16s
fullstack_production_suite / test	4s
integration_tests / test	4s
lint_markdown_files / lint	52s
Coveralls coverage	0s
	6h 8m 3s

Provide feedback