So you want to test every <xsl> in <files> when you expect each <xsl> to transform <input> into <output>?
That is not possible out of the box. One .xspec file is designed to test only one .xsl file.
You probably need to generate one .xspec file for each <xsl>:
test-001.xspec
<x:description stylesheet="test_md.xsl">
<x:scenario label="test_md.xsl should transform input.xml">
<x:context href="input.xml" />
<x:expect label="into output.xml" href="output.xml" />
</x:scenario>
</x:description>
test-002.xspec
<x:description stylesheet="dummy2.xsl">
<x:scenario label="dummy2.xsl should transform input.xml">
<x:context href="input.xml" />
<x:expect label="into output.xml" href="output.xml" />
</x:scenario>
</x:description>
test-003.xspec
...
Thanks,
AirQuick