According to EE spec EE.5.4 Simple Environment Entries:

A simple environment entry is a configuration parameter used to customize an
application component’s business logic. The environment entry values may be one
of the following Java types: String , Character , Byte , Short , Integer , Long ,
Boolean , Double , Float , Class , and any subclass of Enum .

The web.xml descriptor defines it like:

       <env-entry>
	    <env-entry-name>doggie</env-entry-name>
	    <env-entry-type>org.jboss.cdi.tck.tests.definition.bean.types.enterprise.illegal.Dog</env-entry-type>
	</env-entry>

Test should stick to following definition (if it will make sense in the test) I think:

    <env-entry>
        <env-entry-name>helperClass</env-entry-name>
        <env-entry-type>java.lang.Class</env-entry-type>
        <env-entry-value>com.acme.helper.Helper</env-entry-value>
    </env-entry>