How to do a loopback test of a parallel port?
The PassMark web site, the company whose software is being used, provides the loopback connection pin-outs for the relevant types of connectors, including 9 pin DE-9 Serial, 25 pin DB-25 Serial, and 25-pin DB-25 Parallel. 

The pin-out that failed was for DB-25 Serial connectors. The DB-25 parallel port loopback connection is provided:


  
  Data 0 and Error status  (Pin 2 &amp; 15)
  Data 1 and Select status  (3 &amp; 13)
  Data 2 and Paper out status  (4 &amp; 12)
  Data 3 and Acknowledge status  (5 &amp; 10)
  Data 4 and Busy status  (6 &amp; 11)
  


They also provide a diagram, of the male DB-25 connector as seen from its rear:


  


Also relevant, PassMark recommends that the parallel port be set to ECP or EPP mode, and not SPP mode, for loopback testing to work.