tests: Rename build-email test, expand it for expected behavior.
tests: Rename build-email test, expand it for expected behavior.

The key to test is that it flips to the shorter form when it would
get too long.

andersk/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,kou/zulip,zulip/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,eeshangarg/zulip,andersk/zulip,andersk/zulip,zulip/zulip,kou/zulip,kou/zulip,kou/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip