I have applied the application plugin to my build script and set the mainClassName correctly, however as of version 1.0.0 the manifest is not created at all. So there is only an empty META-INF folder in the resulting JAR file.
Also, if I try to run the generated JAR it tells me the following:

Error: Invalid or corrupt jarfile GradleTest-1.0-all.jar

I don't know if this is caused by the missing manifest or something else. Maybe I just configured the plugin wrong?
https://github.com/Minecrell/GradleTest