title: How to resolve Unknown artifact type[test-jar] error in Maven?
body: <p>I got this error while trying to build an ear using Maven.</p>
  
  <pre>
  [ERROR] Failed to execute goal org.apache.maven.plugins:maven-ear-plugin:2.4.2:generate-application-xml (default-generate-application-xml) on project cargooceanear: Failed to initialize ear modules: Unknown artifact type[tes
  t-jar] -> [Help 1]
  org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-ear-plugin:2.4.2:generate-application-xml (default-generate-application-xml) on project cargooceanear: Failed to i
  nitialize ear modules
          at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:216)
          at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
          at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
          at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:108)
          at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:76)
          at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
          at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:116)
          at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:361)
          at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:155)
          at org.apache.maven.cli.MavenCli.execute(MavenCli.java:584)
          at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:213)
          at org.apache.maven.cli.MavenCli.main(MavenCli.java:157)
          at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
          at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
          at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
          at java.lang.reflect.Method.invoke(Method.java:597)
          at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
          at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
          at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
          at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
  Caused by: org.apache.maven.plugin.MojoExecutionException: Failed to initialize ear modules
          at org.apache.maven.plugin.ear.AbstractEarMojo.execute(AbstractEarMojo.java:240)
          at org.apache.maven.plugin.ear.GenerateApplicationXmlMojo.execute(GenerateApplicationXmlMojo.java:85)
          at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:133)
          at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
          ... 19 more
  Caused by: org.apache.maven.plugin.ear.UnknownArtifactTypeException: <b>Unknown artifact type[test-jar]</B>
          at org.apache.maven.plugin.ear.util.ArtifactTypeMappingService.getStandardType(ArtifactTypeMappingService.java:151)
          at org.apache.maven.plugin.ear.EarModuleFactory.newEarModule(EarModuleFactory.java:74)
          at org.apache.maven.plugin.ear.AbstractEarMojo.execute(AbstractEarMojo.java:230)
          ... 22 more
  </pre>