[xsl] Unit tests in XSLT (was: Re: Controlling Debugging Messages)

Talking about debugging, I recently attended a webinar by Oxygen about
unit tests for XSLT (and Schematron). After watching it, I felt guilty
that my XSLT development practice is still not test-driven. Despite of
what was said in the webinar, it seems too much trouble and the thing
that most often requires modification of stylesheets is changes or
hitherto unforeseen constructs in the format of the input XML.

It would be interesting to know if there are readers on this list who
actually make use of units test during XSLT development and what their
experiences are.

Pieter Masereeuw


On 10/15/2018 07:28 PM, Eliot Kimber ekimber(_at_)contrext(_dot_)com wrote:

Yes, in general you want debug messages to be turned off, which is why the 
doDebug parameter default is "false()" in my code.

I didn't think of use-when="$DEBUG or true()"--that would work for a lot of 
my cases but it doesn't handle the case where I want to turn on debugging for 
all the templates that will get called in the course of handing some specific 
input.

So that suggests that my dynamic approach is what I need generally.

Once the code is in place and working then it would be easier to set up a set 
of debugging control variables that reflect different cases or code paths I 
know I might need to debug in the future but during development that doesn't 
really work because of course the code is in flux you don' t necessarily know 
what will be of interest and what won't.

It might work to have per-module static debug controls. I've moved generally 
to using more smaller modules, usually one per distinct mode or set of 
related modes, and that would make it more natural to have global debugging 
for those modes. I'll have to think about that more. 

In practice my debugging pattern isn't a burden--it's something I do whenever 
I set up a new template or add an apply-templates or next-match or 
call-template but it's always felt like there should be a simpler way. 

Cheers,

Eliot
--
Eliot Kimber
http://contrext.com
 

On 10/15/18, 12:11 PM, "Michael Kay mike(_at_)saxonica(_dot_)com" 
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:

    With static variables you can of course have multiple switches but they 
will be statically scoped rather than dynamically scoped. You could use 
multiple variables or you could use flags within a single variable 
(use-when="contains($DEBUG_FLAGS, 'g')").
    
    I have to confess I'm not usually that organized. I tend to have a single 
variable $DEBUG which is false, and then switch on individual debug lines 
using use-when="$DEBUG or true()". I tend to find that debug statements are 
rarely useful once you've solved the bug that they were invented for; except 
in rare cases where you persistently have problems with some particular 
intermediate result passed across a key interface in your application - in 
which case there may be better approaches than xsl:message to monitoring 
what's passed across that boundary.
    
    But I wouldn't recommend anyone to be as disorganised as me.
    
    Michael Kay
    Saxonica
    
    > On 15 Oct 2018, at 17:05, Eliot Kimber ekimber(_at_)contrext(_dot_)com 
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    > 
    > I was just about to post about this.
    > 
    > In my XSLT 2 code I have historically used this pattern:
    > 
    > <xsl:template match="foo">
    >  <xsl:param name="doDebug" as="xs:boolean" tunnel="yes" 
select="false()"/>
    > 
    >  <xsl:if test="$doDebug">
    >   <xsl:message>+ [DEBUG] Handling <xsl:value-of name="concat(name(..), 
'/', name(.))"/>...</xsl:message>
    > 
    >  <xsl:apply-templates>
    >    <xsl:with-param name="doDebug" as="xsl:boolean" tunnel="yes" 
select="$doDebug"/>
    >  </xsl:apply-templates>
    > </xsl:template>
    > 
    > This allows me to selectively turn debugging on and off in specific 
parts of the code but does require this somewhat heavy weight code.
    > 
    > With @use-when, can I get the same level of local control?
    > 
    > That is, with the above, I can add:
    > 
    > <xsl:variable name="doDebug" as="xs:Boolean" select="true()"/>
    > 
    > In any block to turn debugging on just there. 
    > 
    > If I understand the implications of static variables allowed in 
@use-when, the debugging switch is globally all-or-nothing, or at least 
global within a given package.
    > 
    > Is that correct?
    > 
    > If that is correct, is there a better way to do the selective, 
dynamically-controlled debug messaging shown above?
    > 
    > Cheers,
    > 
    > E.
    > 
    > --
    > Eliot Kimber
    > http://contrext.com
    > 
    > 
    > On 10/15/18, 9:08 AM, "Michael Kay mike(_at_)saxonica(_dot_)com" 
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    > 
    >    These days you can do
    > 
    >    <xsl:message use-when="$DEBUG" ....>
    > 
    >    with $DEBUG defined as a static parameter. 
    > 
    >    <xsl:param name="DEBUG" as="xs:boolean" static="true" 
select="false()"/>
    > 
    >    No need for the run-time check with xsl:if.
    > 
    >    You can also use xsl:assert to define assertions. In Saxon, 
assertion checking can be enabled from the command line using -ea.
    > 
    >    Michael Kay
    >    Saxonica 
    > 
    >> On 15 Oct 2018, at 14:54, Dave Pawson 
dave(_dot_)pawson(_at_)gmail(_dot_)com 
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    >> 
    >> MIght even surround it with
    >> <xsl:if test="$debug">
    >> 
    >> To ease insertion / removal when testing?
    >> 
    >> HTH
    >> On Mon, 15 Oct 2018 at 14:31, Wendell Piez 
wapiez(_at_)wendellpiez(_dot_)com
    >> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    >>> 
    >>> Eliot writes:
    >>> 
    >>>> I also depend heavily on using messages to test my assumptions.
    >>> 
    >>>> For example, I might do something like:
    >>> 
    >>>> <xsl:message>+ [DEBUG] jpeg_few={$jpeg_few => string-join(', 
')}</xsl:message>
    >>>> <xsl:message>+ [DEBUG] jpeg_many={$jpeg_many => string-join(', 
')}</xsl:message>
    >>> 
    >>> This is a key technique when developing XSLT. The language is designed
    >>> to "fail gracefully" most of the time -- which puts the burden on the
    >>> programmer to ensure things don't fail catastrophically. :-)
    >>> 
    >>> Cheers, Wendell
    >>> 
    >>> On Sun, Oct 14, 2018 at 7:10 PM Eliot Kimber 
ekimber(_at_)contrext(_dot_)com
    >>> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    >>>> 
    >>>> Looking at the XPath 3 Functions and Operators specification and 
searching on "intersect" (hoping to also find "disjoint") I find this 
discussion:
    >>>> 
    >>>> D.4.2.3 eg:value-except
    >>>> eg:value-except(        $arg1    as xs:anyAtomicType*,
    >>>> $arg2    as xs:anyAtomicType*) as xs:anyAtomicType*
    >>>> This function returns a sequence containing all the distinct items 
that appear in $arg1 but not in $arg2, in an arbitrary order.
    >>>> 
    >>>> XSLT implementation
    >>>> 
    >>>> <xsl:function name="eg:value-except" as="xs:anyAtomicType*">
    >>>> <xsl:param name="arg1" as="xs:anyAtomicType*"/>
    >>>> <xsl:param name="arg2" as="xs:anyAtomicType*"/>
    >>>> <xsl:sequence
    >>>>    select="fn:distinct-values($arg1[not(.=$arg2)])"/>
    >>>> </xsl:function>Which is in 
https://www.w3.org/TR/xpath-functions-31/#other-functions (Appendix D).
    >>>> 
    >>>> So basically
    >>>> 
    >>>> distinct-values($jpeg_few[not(. = $jpeg_many)]
    >>>> 
    >>>> Should give you the answer you seek.
    >>>> 
    >>>> I agree with Mike that being obsessive about putting data types on 
all variables and function return values (and templates when the templates 
should return atomic types or specific element types) will help a lot.
    >>>> 
    >>>> If your code is working without types but failing with them it means 
your code is "working" but probably not for the reasons you think.
    >>>> 
    >>>> Working carefully through the stages of the expressions by setting 
each intermediate result into variable will help a lot.
    >>>> 
    >>>> I also depend heavily on using messages to test my assumptions.
    >>>> 
    >>>> For example, I might do something like:
    >>>> 
    >>>> <xsl:message>+ [DEBUG] jpeg_few={$jpeg_few => string-join(', 
')}</xsl:message>
    >>>> <xsl:message>+ [DEBUG] jpeg_many={$jpeg_many => string-join(', 
')}</xsl:message>
    >>>> 
    >>>> Or if those lists are very long, use count() or get the first n 
items or whatever to make it clear that you're working with the values you 
think you are.
    >>>> 
    >>>> Also, remember that <xsl:value-of> ({} in string result contexts) is 
different from <xsl:sequence>, which returns the actual value, not a string 
representation.
    >>>> 
    >>>> For example, given a variable that is an attribute node, value-of 
will return string value of the attribute but xsl:sequence will return the 
attribute node and Saxon will serialize it as <attribute name="foo" 
value="bar"> (or something similar to that.
    >>>> 
    >>>> It's easy to accidently create a sequence of attributes when what 
you wanted was a sequence of strings (or visa versa) and using xsl:value-of 
can obscure that mistake.
    >>>> 
    >>>> I've also started using the XQuery-required explicating casting of 
values even though XSLT usually lets you get away with implicit casting, 
because it makes it clearer to me what my intent was (and makes it easier to 
copy XPath expressions into XQuery, if that's something you need to do).
    >>>> 
    >>>> Cheers,
    >>>> 
    >>>> Eliot
    >>>> --
    >>>> Eliot Kimber
    >>>> http://contrext.com
    >>>> 
    >>>> 
    >>>> On 10/14/18, 3:53 PM, "Dave Lang 
emaildavelang(_at_)gmail(_dot_)com" 
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
    >>>> 
    >>>>> That error can only come from an expression that calls tokenize(). 
It's therefore clearly not your declaration of jpgs_in_xml_not_directories 
that's at fault.
    >>>> 
    >>>>   Fair enough - but when I run the transformation without that 
declaration
    >>>>   everything works fine. Is there something I can do to the 
variables that
    >>>>   are included in it to make the declaration work?
    >>>> 
    >>>> 
    >>>> 
    >>>> 
    >>> 
    >>> 
    >>> 
    >>> --
    >>> Wendell Piez | http://www.wendellpiez.com
    >>> XML | XSLT | electronic publishing
    >>> Eat Your Vegetables
    >>> _____oo_________o_o___ooooo____ooooooo_^
    >>> 
    >> 
    >> 
    >> 
    >> -- 
    >> Dave Pawson
    >> XSLT XSL-FO FAQ.
    >> Docbook FAQ.
    >> 
    > 
    > 
    > 
    >

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