In most use-cases, the hibernate4-maven-plugin is used to create a test-database automatically. In this use-cases, it is very likely, that it will result in mistakes/errors, if the goal is executed, when the tests are skipped. For example, one might manually overwrite the database-url with the url of the production-database, in order to run other tests, like starting a local webserver with the jetty-maven-plugin. If the export-goal would be executed in such a scenario, it might erase the hole production-database, which is not very desireable.

Because of this, the configuration-parameter skip defaults to the value of the proptery maven.test.skip. This way, the execution of the hibernate4-maven-plugin is skipped automatically, when the tests are skipped. Think of it as a build-in security-belt.

If you do not like that, because you need the plugin to always execute the export-goal, even if the tests are skipped you can configure that explicitly, by setting the configuration-parameter skip to false:

<plugin>
  <groupId>de.juplo</groupId>
  <artifactId>hibernate4-maven-plugin</artifactId>
  ...
  <configuration>
    <skip>false</skip>
  </configuration>
</plugin>

Or, if you want the export-goal to be executed by default and to be skipped if you say so, you can bind the value of the configuration-parameter skip to a custom property. For example:

<plugin>
  <groupId>de.juplo</groupId>
  <artifactId>hibernate4-maven-plugin</artifactId>
  ...
  <configuration>
    <skip>${foo.bar}</skip>
  </configuration>
</plugin>

This way, the export-goal would be skipped, if you set the property foo.bar to true. For example, if you specify -Dfoo.bar=true on the command-line.