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If you can live with a test environment that uses the latest snapshots, the java-idp-testbed project launches an embedded Jetty container to run the snapshot IdP locally on port 8443. Modifying the POM to reference any extension projects of your own may (emphasis on may) allow you to run those extensions by configuring the IdP to use them.
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A README file in the project outlines how to run the testbed with maven or EclipseEclipse, simply by running Main.java as a Java Application.