Unit Testing: groovy.lang.MissingMethodException upon calling g.message() in a TagLib

In http://blog.springsource.com/2011/06/07/countdown-to-grails-1-4-unit-testing/, Peter states that "The standard Grails tags will just work and you can enable other tags by simply calling mockTagLib() with the relevant TagLib class."

However, tests still fail with the following errors:

groovy.lang.MissingMethodException: No signature of method: myproj.MyprojTagLib.message() is applicable for argument types: (java.util.LinkedHashMap) values: [[code:taglib.thetag.title, default:Default Message, ...]]
Possible solutions: isCase(java.lang.Object)
at myproj.MyprojTagLib$_closure14.doCall(MyprojTagLib.groovy:379)
at myproj.MyprojTagLibTests.testOutputIsFreeOfAnyInlineScripts(MyprojTagLibTests.groovy:56)

// Line 379 of MyprojTagLib.groovy:
def title = (attrs?.remove('title') ?: message(code:"taglib.thetag.title", default:"Default Message", locale: dataLocale)).encodeAsHTML()

// Line 56 of MyprojTagLibTests.groovy:
assert !(tagLib.theTag(name:'p'){"Arbitrary Body"}.toString()).contains("script")

Is this a bug, or is the according feature simply yet to be implemented?