if seek(bintoc(m.nMonat) + bintoc(m.nBeleg), [z_Image]) assert z_Image.MONAT == m.nMonat and z_Image.BELEG == m.nBeleg ...because the test is affordable and so it would be unwise not to do it. However, tests like these can only uncover cases where an index finds wrong things; they cannot detect other modes of failure like positioning on the wrong record or failing to find a key that is actually present.