adding new data to XML file, updating attribute counter, via XSLT

I want add some data to the end of an existing XML file.
In a simplified form my original XML file looks like this

<?xml version="1.0"?>
<file>
  <table>
    <comment/>
    <xref>yes</xref>
    <test key="1">
      <name>nameA</name>
      <type>type7</type>
    </test>
    <test key="2">
      <name>nameC</name>
      <type>type9</type>
    </test>
  </table>
</file>

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I want to add a new test element group with name=nameG and type=type4
I want to add it after all the existing test elements
I don't know how many test elements there are in the original XML files although i do know that value of the key attribute will match the test element count i.e. 3rd test element would have key="3"

So, knowing that I want to add a  new test element group with name=nameG and type=type4 I would want to end up with this:

<?xml version="1.0"?>
<file>
  <table>
    <comment/>
    <xref>yes</xref>
    <test key="1">
      <name>nameA</name>
      <type>type7</type>
    </test>
    <test key="2">
      <name>nameC</name>
      <type>type9</type>
    </test>
    <test key="3">
      <name>nameG</name>
      <type>type4</type>
    </test>
  </table>
</file>

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I need a way to add this new information in via XSLT.
Can anyone point me in the right direction of how to do this?

Thanks.