notifications: Add tests for `relative_to_full_url()` function.
notifications: Add tests for `relative_to_full_url()` function.

Fixes: #6544.

punchagan/zulip,synicalsyntax/zulip,andersk/zulip,rishig/zulip,Galexrt/zulip,tommyip/zulip,punchagan/zulip,kou/zulip,hackerkid/zulip,shubhamdhama/zulip,eeshangarg/zulip,kou/zulip,dhcrzf/zulip,kou/zulip,punchagan/zulip,Galexrt/zulip,hackerkid/zulip,tommyip/zulip,zulip/zulip,eeshangarg/zulip,brainwane/zulip,mahim97/zulip,Galexrt/zulip,dhcrzf/zulip,punchagan/zulip,rht/zulip,jackrzhang/zulip,tommyip/zulip,andersk/zulip,synicalsyntax/zulip,zulip/zulip,timabbott/zulip,jackrzhang/zulip,eeshangarg/zulip,amanharitsh123/zulip,timabbott/zulip,rht/zulip,hackerkid/zulip,kou/zulip,brockwhittaker/zulip,verma-varsha/zulip,dhcrzf/zulip,rishig/zulip,amanharitsh123/zulip,Galexrt/zulip,brainwane/zulip,dhcrzf/zulip,brockwhittaker/zulip,brockwhittaker/zulip,timabbott/zulip,amanharitsh123/zulip,amanharitsh123/zulip,punchagan/zulip,Galexrt/zulip,Galexrt/zulip,tommyip/zulip,brockwhittaker/zulip,verma-varsha/zulip,amanharitsh123/zulip,verma-varsha/zulip,showell/zulip,Galexrt/zulip,eeshangarg/zulip,tommyip/zulip,brainwane/zulip,synicalsyntax/zulip,tommyip/zulip,rishig/zulip,showell/zulip,jackrzhang/zulip,dhcrzf/zulip,synicalsyntax/zulip,kou/zulip,verma-varsha/zulip,rishig/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,verma-varsha/zulip,hackerkid/zulip,synicalsyntax/zulip,timabbott/zulip,hackerkid/zulip,shubhamdhama/zulip,mahim97/zulip,showell/zulip,andersk/zulip,amanharitsh123/zulip,punchagan/zulip,mahim97/zulip,timabbott/zulip,jackrzhang/zulip,brainwane/zulip,mahim97/zulip,tommyip/zulip,hackerkid/zulip,dhcrzf/zulip,showell/zulip,andersk/zulip,shubhamdhama/zulip,rishig/zulip,kou/zulip,zulip/zulip,jackrzhang/zulip,jackrzhang/zulip,rishig/zulip,andersk/zulip,andersk/zulip,shubhamdhama/zulip,brockwhittaker/zulip,brainwane/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,zulip/zulip,punchagan/zulip,zulip/zulip,showell/zulip,synicalsyntax/zulip,mahim97/zulip,kou/zulip,verma-varsha/zulip,brainwane/zulip,brockwhittaker/zulip,rht/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rishig/zulip,rht/zulip,dhcrzf/zulip,eeshangarg/zulip,rht/zulip,jackrzhang/zulip,rht/zulip,mahim97/zulip,showell/zulip,rht/zulip,timabbott/zulip,showell/zulip,shubhamdhama/zulip,brainwane/zulip