IDL 8.4 adds a new routine, CODE_COVERAGE (docs), which returns information about the lines of a routine that have been executed. Using CODE_COVERAGE is fairly straight-forward — you do not need to enable code coverage. Just call CODE_COVERAGE at any time to find the lines of a routine that have been executed. Note that the routine must have been at least compiled before you call CODE_COVERAGE (even if you are clearing the status of the routine). Also, pay particular definition of the definition of a “line of code” in the docs, e.g., empty lines, comments, and END statements do not count. Between the return value and the output from the EXECUTED keyword, you should get all the lines of code in a routine.

CODE_COVERAGE adds another useful developer tool to the timing routines like PROFILER1, TIC and TOC. I think CODE_COVERAGE has a range of uses, but most interesting for me is the ability to determine the coverage of your unit test suite, i.e., how much of my code base is executed by my test suite?

I have already implemented some basic test coverage information in my unit testing framework, mgunit. For example, mgunit can now tell me that I’m missing coverage of a few lines in the helper routines for MG_SUBS:

"mg_subs_ut" test case starting (5 tests)
  test_basic: passed (0.000223 seconds)
  test_derived: passed (0.000354 seconds)
  test_derived2: passed (0.000369 seconds)
  test_derived_perverse: passed (0.000477 seconds)
  test_not_found: passed (0.000222 seconds)
Test coverage: 90.5%
  Untested lines
    mg_subs_iter: lines 135
    mg_subs_getvalue: lines 72-73, 79
  Completely covered routines
    mg_subs
Results: 5 / 5 tests passed, 0 skipped

This means that after the unit tests have been run, line 135 from MG_SUBS_ITER and lines 72-73, 79 from MG_SUBS_GETVALUE have not been executed. This is useful (though not complete) information for determining if you have enough unit tests. Grab mgunit from the master branch on GitHub to give it a try (see mglib for an example of unit tests that take advantage of it). I’m not sure of the exact format for displaying the results, but I am fairly certain of the mechanism for telling the unit tests which routines it is testing (an ::addTestingRoutine method). I intend to start using this for the unit tests of my products GPULib and FastDL soon!


  1. There is also a CODE_COVERAGE keyword to PROFILER now that displays the number of lines of a routine that were executed.