Implement unit tests for the `RefSetCache` primitive
Implement unit tests for the `RefSetCache` primitive

This primitive did not have unit test coverage yet, which is important
for upcoming refactoring of the primitive.

mozilla/pdf.js,Shoobx/pdf.js,xavier114fch/pdf.js,timvandermeij/pdf.js,macroplant/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,mozilla/pdf.js,mozilla/pdf.js,xavier114fch/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,Shoobx/pdf.js,Snuffleupagus/pdf.js,timvandermeij/pdf.js,showpad/mozilla-pdf.js,caremerge/pdf.js,macroplant/pdf.js,Snuffleupagus/pdf.js,caremerge/pdf.js,macroplant/pdf.js,showpad/mozilla-pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js