A management or leadership assessment center is a series of tests, interviews, simulations, and exercises designed to predict how well a management candidate will perform in a specific role. For you sports fans, think of the NFL Combine, used to assess college players to help teams decide who to pick for the draft.
Unfortunately, this type of employment assessment can be costly. This cost is the number one reason why many companies don’t use outside firms. Such testing is usually reserved for senior management positions, given the potential risk if one of these high-level managers doesn't work out.
For a middle-management hire, use a well designed internal development and succession planning system. By carefully grooming and observing your own pool of internal candidates, you won’t need to rely on external assessments and experts. Besides, external hires are also usually more expensive and riskier than an internal promotion.