As a Tier 2 sponsor, you should expect a compliance visit from UK Visas & Immigration (UKVI) at some point during the validity of your licence. Such visits can be announced or unannounced, but the purpose is the same - to establish whether you are complying with your sponsor duties.
The key to a successful audit is preparation! You should carry out internal audits regularly to check your HR team is aware of its obligations and to identify any potential breaches early. Remember: if UKVI is not satisfied with your performance, it could suspend, downgrade or revoke your licence.