XSL - check a mapping using key() against a list of items

what I would like to achieve is a solution where an existing mapping in XSL is used to verify that a number of items are supported. Items to be tested are stored in an attribute (separated by whitespace).

<items>
  <item name="item1" supported="true">
  <item name="item2" supported="false">
  <item name="item3" supported="true">
</items>

We are using an additional XML file stating some test cases.

<testsuite name="suite1">
  <testcases>
    <testcase name="test1" required_items="item1 item3">
  </testcases>
  <testcases>
    <testcase name="test2">
  </testcases>
</testsuite>

Question: How could we achieve the following pseudo code?

FOREACH testcase
  IF "required_items" is EMPTY
  THEN
    print TEST_TO_RUN += testcase
  ELSE
    IF "required_items" are SUPPORTED
      print TEST_TO_RUN += testcase
    END IF
  END IF
END FOREACH