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All the Perl that's Practical to Extract and Report

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use_ok is not ok. 3 Comments More | Login | Reply /

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  • I see the value of having a test script which reality-checks that everything compiles, especially if there are big gaps in a test suite.

    But I don't see what's wrong with "use_ok()" for a module that you neede to "use" anyway. It's hardly any more syntax. What's the harm?

    • First, here's the general 'correct' incantation:

      BEGIN {
          use_ok 'Some::Module' or die "Cannot use Some::Module";
      }

      If the module is not used in a "BEGIN" block, compile-time behavior is ignored (e.g., exported functions may alter how your code parses).

      If you don't have the 'or die' (or BAIL_OUT), things can get even worse. If the module fails to load, but most of it compiled, you can get partially compiled code loaded. Your 'use_ok' failure may scroll off the screen but failures show up much later in the test program run (this is a very subtle bug and one which once caused and fellow programmers hours of debugging grief).

      Finally, where's the canonical spot for that use_ok statement? I often see test suites where I open up four of five different test modules, each of which has identical use_ok statements at the top. Testing something more than once doesn't make it more true. However, if you think you need to test 'use'ing a module more than once -- perhaps it won't load if another module loads -- the you probably have some bad coupling in your code and your "use Some::Module" statement in the test will catch the error anyway. It's annoying to have to write that entire BEGIN block every time I want to use a module. Just putting it into one "load" test means I don't have to worry about that any more.

      • So I would say it summarizes like this:

        If "use" a module it fails, the test grinds to a halt, which is nearly always a reasonable result.

        With "use_ok", the test may /continue/ causing unexpected results later on, because the module is not loaded, or worse, partially loaded.

        Thanks for your clarification, Ovid.

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