Monday, April 27, 2009

XQuery Unit Tests

I had a fright last week - Wolfgang asked for a copy of the test harness I'd used to evaluate different implementations of a lookup table. This is code I wrote some time ago, tinkered with, good enough for our internal use but ... well pretty bad code.

I have to confess here that as a lone XQuery programmer, my code doesn't get the level of critique it needs. The Wikibook has been disappointing in that regard: I've published thousands of lines of code there and there has not been a single criticism or improvement posted. Typos in the descriptions are occasionally corrected by helpful souls, graffiti erased by others but as a forum for honing coding skills - forget it. In my task as project leader on our FOLD project (now coming to an end), I see and review lots of my students' code as well as the code Dan McCreary contributes to the WikiBook so I do quite a bit of reviewing. However I am only too conscious of the lacunae in my XQuery knowledge which perhaps through over kindness or because everyone is so busy, remain for too long. I'm envious of my agile friends who have been pair-programming for years. Perhaps there should be a site to match up lonely programmers for occasional pairing.

Anyway the test suite got a bit of work on it one day last week and its looking a bit better.

Here is a sample test script . As a test script to test the test runner it has the unusual property that some failed tests are good since failing is what's being tested. Here is it running.
Here is another, used to test the lookup implementations and one to test the geodesy functions.

Version 1 of the test runner executed tests and generated a report in parallel. A set of tests may have a common set of modules to import, prefix and suffix code. For each test, modules are dynamically loaded, the code concatenated and then evaled inside a catch.

let $extendedCode := concat($test/../prolog,$test/code,$test/../epilog)
let $output := util:catch("*",util:eval($extendedCode),Compile error)

The output is compared with a number of expected values. Comparison may be string-based, element-based, substring present or absent. (I also need to add numerical comparison with defined tolerance.) A test must meet all expectations to pass.

To get a summary of the results requires either running the sequence of tests recursively or constructing the test results as a constructed element and then analysing the results. Recursion would be suitable for a simple sum of passes and fails, but it closely binds the analysis to the testing. An intermediate document decouples testing from reporting, thus providing greater flexibility in the analysis but requiring temporary documents.

So version 2 constructed a sequence of test results, and then merged these results with the original test set to generate the report. Collating two sequences is a common idiom which in functional languages must either recurse over both, or iterate over one sequence whilst indexing into the other, or iterate over a extracted common key and index into both. The reporting is currently done in XQuery but it should be possible to use XSLT. Either the collating would need to be done before the XSLT step or XSLT would have the collating task. Not a happy situation.

So last week in comes version 3. Now the step which executes the tests augments each test with new attributes (pass, timing) and elements (output) and similarly each expectation with the results of its evaluation so that one single, enhanced document is produced, with the same schema as the original [the augmented data has to be optional anyway since some tests may be tagged to be ignored]. Transformation of the complete document to HTML is then straightforward either in line,in a pipeline with XQuery or XSLT. The same transformation can be run on the un-executed test set.

Augmenting the test set is slightly harder in XQuery than it would be in XSLT. For example, after executing each test, the augmented test is recreated with:

element test {
attribute pass {$pass},
attribute timems {$timems},
$test/(* except expected),
element output {$output},

This approach means that, once again, handling the construction of temporary documents is a key requirement for XQUery applications.

But I'm still not quite happy with version 3. As so often I'm struggling with namespaces in the test scripts - now where's my pair?


Joe said...


This is really interesting! As an avid user / fan of the XQuery wikibook, it seems to me that this would make an excellent entry under "Development Tools" or "Debugging XQuery"? I'd really like to learn more about how to create my own unit tests. Would you consider putting the .xq code up on a wikibook page?

Thanks for all of your hard work on the wikibook - I hope to return to contributing content to it and hope to be able to review too.

- Joe

chris wallace said...

Hi Joe

Thanks for the kind words - I'll put the code up in the Google Code XQuery examples project this weekend


tony525 said...

just caught the 'lacunae' reference ... nice