1. An integrated circuit, comprising: operation circuitry having nodes and external terminals for input and output of signals during normal operation, a test controller connected to at least a first one of said external terminals for receiving signals and for providing output signals during a test operation, a test register for containing signals representative of selected tests to be performed connected to said test controller and at least a second one of said external terminals and responsive to said output signals of said test controller for enabling selected tests, and wherein said test controller and test register are operable to enable said selected tests without disturbing normal operation of the operation circuitry.