tests: Add test for sending group mentions in messages.
tests: Add test for sending group mentions in messages.

brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,dhcrzf/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,synicalsyntax/zulip,showell/zulip,kou/zulip,andersk/zulip,jackrzhang/zulip,shubhamdhama/zulip,tommyip/zulip,showell/zulip,kou/zulip,andersk/zulip,punchagan/zulip,brainwane/zulip,tommyip/zulip,showell/zulip,showell/zulip,synicalsyntax/zulip,brainwane/zulip,jackrzhang/zulip,jackrzhang/zulip,dhcrzf/zulip,rishig/zulip,dhcrzf/zulip,punchagan/zulip,jackrzhang/zulip,shubhamdhama/zulip,kou/zulip,zulip/zulip,rishig/zulip,andersk/zulip,dhcrzf/zulip,timabbott/zulip,brainwane/zulip,rht/zulip,tommyip/zulip,timabbott/zulip,showell/zulip,tommyip/zulip,brainwane/zulip,dhcrzf/zulip,eeshangarg/zulip,jackrzhang/zulip,showell/zulip,synicalsyntax/zulip,rht/zulip,dhcrzf/zulip,rishig/zulip,brainwane/zulip,rht/zulip,eeshangarg/zulip,rht/zulip,shubhamdhama/zulip,shubhamdhama/zulip,timabbott/zulip,rishig/zulip,kou/zulip,rishig/zulip,hackerkid/zulip,zulip/zulip,jackrzhang/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,synicalsyntax/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,shubhamdhama/zulip,andersk/zulip,timabbott/zulip,shubhamdhama/zulip,rishig/zulip,punchagan/zulip,shubhamdhama/zulip,tommyip/zulip,zulip/zulip,kou/zulip,showell/zulip,zulip/zulip,timabbott/zulip,rht/zulip,eeshangarg/zulip,synicalsyntax/zulip,tommyip/zulip,eeshangarg/zulip,hackerkid/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,rishig/zulip,zulip/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,synicalsyntax/zulip,tommyip/zulip,rht/zulip,punchagan/zulip,dhcrzf/zulip,jackrzhang/zulip,brainwane/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,andersk/zulip