How to ignore XML declaration differences with XmlUnit?

Question

How can I configure XmlUnit.Net to ignore the XML declaration when comparing two documents?

Assume I have the following control document:

<?xml version="1.0" encoding="utf-8"?>
<a><amount>1</amount></a>

Which I want to compare with:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<a><amount>1</amount></a>

The comparison should result in no differences.

My expectation would be that using a NodeFilter like so should work, but it doesn't:

var diff = DiffBuilder.Compare(control)
    .WithTest(test)
    .WithNodeFilter(n => n.NodeType != XmlNodeType.XmlDeclaration)
    .Build();

diff.Differences.Count().Should().Be(0);

The assertion fails with two differences - one for the encoding (different casing) and another for the standalone attribute. I'm not interested in any.

Whether I say n.NodeType != XmlNodeType.XmlDeclaration or n.NodeType == XmlNodeType.XmlDeclaration makes no difference.

I am using XMLUnit.Core v2.5.1.

Answer 1

NodeFilter only applies to nodes that are children of other nodes (returned by XmlNode.ChildNodes). Unfortunately this is not the case for the document type declaration, which probably is a bug.

In your case you want to tweak the DifferenceEvaluator and downgrade the differences you are not interested in. Something like

DifferenceEvaluators.Chain(DifferenceEvaluators.Default,
    DifferenceEvaluators.DowngradeDifferencesToEqual(ComparisonType.XML_STANDALONE, ComparisonType.XML_ENCODING))

would swallow the differences.

Maybe you don't want to just count the differences but also look at their severity. The difference in encoding would be a "similar" difference, while the different values of standalone are critical.