A memory-testing circuit configured to perform a test of reference bits in a memory. In a read operation, outputs of data bit columns are compared with one or more reference bit columns. The memory-testing circuit comprises: a test controller and association adjustment circuitry configurable by the test controller to associate another one or more reference bit columns or one or more data bit columns with the data bit columns in the read operation. The test controller can determine whether the original one or more reference bit columns have a defect based on results from the two different association.