A method of testing a multi-core network processor comprises placing the multi-core network processor in an online environment. A test is performed on a core of the multi-core network processor when the core is idle, and the core is released from the test when it is completed and resumes processing data in the online environment. In another embodiment, a network processor comprises a computer readable instructions module and a processing core. The computer readable instructions module is configured to store test instructions, and the processing core is configured to operate in an online environment and execute the test instructions to test the processing core when the processing core is idle. In yet another embodiment, an apparatus comprises a multi-core network processor that is configured to execute test instructions to perform a test on a core of the multi-core network processor when the core is idle.