Question: how online checker works?

[M@K@K]

anyone can give me details on how online dumps checker works.
if it was tested (checked) for 1$ for example to see if live ( approved) what happen?
it is tested on a pos? virtual pos?
the 1$ transaction will be shown on original card holder's transaction's card page?
can someone explain please?
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can someone help me with detailed explanation please.
i need to get some knowledge.