A test apparatus for generating reference scan chain test data comprises a test pattern generator and an output data modifier. The test pattern generator modifies a scan chain test input bit sequence by replacing a predefined number of start bits of the scan chain test input bit sequence by a predefined start bit sequence. Further, the test pattern generator provides the modified scan chain test input bit sequence to a device under test. The output data modifier modifies a scan chain test output bit sequence received from the device under test and caused by the modified scan chain test input bit sequence. The scan chain test output bit sequence is modified by replacing a predefined number of end bits of the scan chain test output bit sequence by a predefined end bit sequence to obtain the reference scan chain test data.