Test case for "str:concat" doesn't even reference "str:concat"

Now I'm really confused.  The test case for "str:concat" that I
downloaded from the EXSLT web site, which is "str.concat.1.xsl", doesn't
even reference "str:concat".  It's just:

<?xml version="1.0"?>
<xsl:stylesheet version="1.0" 
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:str="http://exslt.org/strings"
                extension-element-prefixes="str">
<xsl:template match="/">
   <xsl:value-of select="." /><br/>
   <xsl:value-of select="/a/c" />
</xsl:template>
</xsl:stylesheet>

Am I misunderstanding something here?