The source files are tut7.tv, and counter1.v. This exercise is identical to exercise 9, except that the internal signal is now declared as bidirectional; the testbench both writes to (forces) the internal signal, and reads it back. The read-back operations result in two extra passes as compared to exercise 9:

  (Log) (220 ns) 22 vectors executed (23 passes, 0 fails)