xslt :how to check whether the value of a string variable is Yes or No?

[prao2005]

how to check whether the value of a string variable is Yes or No?

xsl;variable name="test1" select="DBE:OBJECT/DBE:ATTRIBUTE[@name='test1']/DBE:String"/>
xsl;variable name="test2" select="DBE:OBJECT/DBE:ATTRIBUTE[@name='test2']/DBE:String"/>

xsl;choose>
xsl;when test="$test1 = 'Yes'>
    xsl;apply-templates select="YES"/>
/xsl;when>
xsl;when test="$test2 = 'Yes'>
    xsl;apply-templates select="Invalid"/>
/xsl:when>
xsl;otherwise>
     xsl;apply-templates select="DBE:OBJECT/DBE:ATTRIBUTE[@name='test3']/DBE:String"/>
/xsl;otherwise>
/xsl;choose>

Please let me know what is wrong in the above?