grails test-app throwing a NPE (2.3.4)

[staticnull]

[08:47:49.092] ERROR [main] resource.ResourceProcessor - Unable to load resources
java.lang.NoClassDefFoundError: com/yahoo/platform/yui/compressor/CssCompressor
at java.lang.Class.privateGetDeclaredMethods(Class.java:2570)
at java.lang.Class.getDeclaredMethods(Class.java:1855)
at org.codehaus.groovy.util.LazyReference.getLocked(LazyReference.java:46)
at org.codehaus.groovy.util.LazyReference.get(LazyReference.java:33)
at org.codehaus.groovy.util.LazyReference.getLocked(LazyReference.java:46)
at org.codehaus.groovy.util.LazyReference.get(LazyReference.java:33)
at com.blockconsult.yuiminifyresources.YuiCssMinifyResourceMapper.map(YuiCssMinifyResourceMapper.groovy:28)
at org.grails.plugin.resource.mapper.ResourceMapper.invoke(ResourceMapper.groovy:139)
at org.grails.plugin.resource.mapper.ResourceMapper.invokeIfNotExcluded(ResourceMapper.groovy:128)
at org.grails.plugin.resource.ResourceProcessor.applyMappers(ResourceProcessor.groovy:575)
at org.grails.plugin.resource.ResourceProcessor.prepareResource(ResourceProcessor.groovy:542)
at org.grails.plugin.resource.ResourceProcessor$_prepareSingleDeclaredResource_closure13.doCall(ResourceProcessor.groovy:599)
at org.grails.plugin.resource.util.ResourceMetaStore.addDeclaredResource(ResourceMetaStore.groovy:29)
at org.grails.plugin.resource.ResourceProcessor.prepareSingleDeclaredResource(ResourceProcessor.groovy:597)
at org.grails.plugin.resource.ResourceProcessor$_prepareResourceBatch_closure15.doCall(ResourceProcessor.groovy:622)
at org.grails.plugin.resource.ResourceProcessorBatch.each(ResourceProcessorBatch.groovy:8)
at org.grails.plugin.resource.ResourceProcessor.prepareResourceBatch(ResourceProcessor.groovy:618)
at org.grails.plugin.resource.ResourceProcessor.resourcesChanged(ResourceProcessor.groovy:777)
at org.grails.plugin.resource.ResourceProcessor.loadModules(ResourceProcessor.groovy:773)
at org.grails.plugin.resource.ResourceProcessor.reloadAll(ResourceProcessor.groovy:1006)
at ResourcesGrailsPlugin$_closure3.doCall(ResourcesGrailsPlugin.groovy:165)
at TestApp$_run_closure1.doCall(TestApp:99)
at TestApp$_run_closure1.doCall(TestApp.groovy:32)
Caused by: java.lang.ClassNotFoundException: com.yahoo.platform.yui.compressor.CssCompressor
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 23 more
| Error Fatal error running tests: null (Use --stacktrace to see the full trace)
| Tests FAILED - view reports in /Users/ekinsella/development/projects/groovymn/hackingmn-website/target/test-reports
| Error Error executing script TestApp: java.lang.NullPointerException (Use --stacktrace to see the full trace)