[lib] add emoji tests file

Summary: Readding emojis test file. For some reason when I landed D6398 this file got deleted.

Test Plan:
flow and ran tests with the following results

Reviewers: atul, tomek, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6412