This paper presents an explanation of the program design of the three separate Pascal-language programs which comprise UCLA's Diagnostic Testing Package "DX." The three parts of the DX test package are three closely interrelated programs--Editest, Runtest, and Summary. Editest serves the following functions: (1) the creation of a suitable direct-access file of textual material for each test module; (2) the automatic creation of special files known as cue-files, which provide the requisite program pointers that allow the testing process to be adaptive, and error types to be found within a test; (3) the editing of the direct-access file of text using a simple line-oriented editor; and (4) the review of a specified direct-access file of test materials one screen at a time. The program Runtest is the computive central manager of the adaptive testing sequence, and the student response file is evaluated by the Summary program. Flow charts for each program and test administration are given. Samples are included showing: (1) test item layout; (2) location cue files; and (3) test performance summaries. The Pascal listings for each of the three programs are also appended. (LMO)