#17 use tolerance for floating point values in XML

[Ken Estes]

We produce XML which has numerical values scattered through out the
XML both in nodes and attributes.

<svg xmlns="http://www.w3.org/2000/svg" width="0.085in" height="0.085in">
<text text-anchor="end" y="92" x="15">36</text>
<fo:block-container height="2pc" width="46.5pc" left="2.5pc" top="64pc">

The numerical values can be produced by computations which are carried
out in software or hardware. Because of round off errors we need to
have a custom string equals function which will allow for round off in
the numeric portions of the string.

Enclosed please find a file which will perform such numeric comparisons.

Here is my suggestion for how to hook it into XMLUnit.

/**
* Test two non-null values for inequality
* @param expected
* @param actual
* @return TRUE if the values are not equals() equal (taking whitespace
* into account if necessary)
*/
private boolean unequalNotNull(Object expected, Object actual) {
boolean bothStrings = (expected instanceof String
&& actual instanceof String);
if (!bothStrings) {
return !(expected.equals(actual));
}

String expectedString = (String) expected;
String actualString = (String) actual;

if (XMLUnit.getIgnoreWhitespace()) {
expectedString = expected.trim();
actualString = actual.trim();
}
if (XMLUnit.getNormalizeWhitespace()) {
expectedString = normalizeWhitespace(expectedString);
actualString = normalizeWhitespace(actualString);
}

if (XMLUnit.getTolerantNumericCompare) {
return !StringCmpNumericTolerance.equals(expected,actualString);
}
return !expectedString.equals(actualString);
}

[Ken Estes]

string comparison with tolerance for floats

[Stefan Bodewig]

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Hi Ken,

to be honest I feel we would be stretching XMLUnit quite a bit if we added special purpose options like handling of numeric values to its core. The same could be said for case insensitive comparisons of element and attribute names (HTML as a use-case) or texts and so on.

It should be possible to use a DifferenceListener of your own that wrapped whatever DifferenceListener would get used normally and performed some special sort of comparision for ATTR_VALUE Differences. We might even add such a DifferenceListener in XMLUnit's examples package.

[Ken Estes]

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It would be simplest for my case to wrap the standard DifferenceEngine with another class, because what I wish to
change is the method unequalNotNull(Object expected, Object actual) in this class. However this is difficult
with the current code structure.

1) The DifferenceEngine class has methods which are private/final and this makes extending the object diffcult

2) it is not clear how to pass my new class into the Diff(,) object to be used instead of the normal differenceEngine.

I was hoping to use the diff constructor Diff(Document controlDoc, Document testDoc, DifferenceEngine comparator)
But this is a tangle of dependencies. My DifferenceEngine needs to be constructed first, so that I could pass it into the Diff. However to construct my class I need to pass in the Diff (this is the only class which
implements ComparisonController) that it will be used for as a parameter. I suggest that you should separate the
implementations of DifferenceListener, ComparisonController and not keep diff as an implementation of both since
the dependency issues for both are quite separate.

And Worse there is no setDifferenceEngine() method for Diff() so that I could create my own DifferenceEngine
after the diff was constructed (and pass in the already constructed diff as a parameter) then override the default difference engine with what I just created.

In sort overriding the DifferenceEngine class is quite difficult.

[Stefan Bodewig]

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Like I said, this can be done using a DifferenceListener.

A simplisitic one (for usage see its unit test) is now part of the examples package.

http://xmlunit.svn.sourceforge.net/viewvc/xmlunit?view=rev&revision=249