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It's not an engine, there are no moving parts. You do not break in electronics.
I don't think the OP meant "break in." I think he basically meant "test." If a card is DOA, it's pretty obvious immediately, so take a few test photos and read them elsewhere, and you've done what you can do. If it's going to fail later, there's no telling when that will be, so if a testing period is of any use at all, it's very short.
Using a dual-card-slot body helps mitigate risk.