When adding an Email-Ext post-build action, managed file templates can be used by pre-pending "managed:" when calling the script.

Unfortunately the same is not true when using the Template Testing page.

When trying to test a managed template the following exception is seen:

<pre>
Caused by: java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:148)
at java.util.AbstractList.add(AbstractList.java:108)
at hudson.plugins.emailext.EmailExtTemplateAction.getTemplateConfigProviders(EmailExtTemplateAction.java:94)
at hudson.plugins.emailext.EmailExtTemplateAction.checkForManagedFile(EmailExtTemplateAction.java:75)
at hudson.plugins.emailext.EmailExtTemplateAction.doTemplateFileCheck(EmailExtTemplateAction.java:59)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:298)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:161)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:96)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:120)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:728)
... 70 more

</pre>