How are ejection seats tested? How does a company like Martin Baker, evaluate the safety of their ejection seats. Are there any standard metrics or tests that exist? If not, what would be the suggested tests to be performed before they release the seat.

Edit: I am more interested in the type of data they collect from the tests. If I were to create a ejection seat on my own, what quantities would I use it to compare it against Martin Baker's seat?
Martin-Baker tests their seats in an actual aircraft. They have, for some time now, used a Gloster Meteor to test their designs as discussed in this question. They also have a high speed sled at their facility for such tests.. 0-0 tests are easier to pull off since there is no moving component.

Individual components like explosive bolts or handles are likely tested like any other engineering component, in a test facility.