It is essential that you provide some form of integration testing for your projects and the Invoker Plugin tries to make is easy for you to create integration tests for your Maven Plugins, new Lifecycles, or any other type of Maven component that you've created. Currently the Invoker Plugin forks Maven to execute the specified projects, but it is hoped that soon we will integrate the Maven Embedder into the mix to allow you run your projects in process for great speed.
Sometimes you might want to test that error conditions are properly dealt with, i.e. fail a build. To assert a failure for a particular IT project, put the following setting into the properties file denoted by the plugin's invokerPropertiesFile parameter: invoker.buildResult=failure. Now, the failure of the IT build will be interpreted as a test success. Likewise, a successful IT build will be considered a test failure.
If you want to avoid copy&paste of lengthy code snippets within the hook scripts, you can move this code into a regular Java class. More precisely, you would place this utility code somewhere in your test source tree and set the plugin parameter addTestClassPath to true. For more details, please see the example Accessing Test Classes.
This is not supported in the plugin configuration but rather on a per project basis by means of the invoker properties. This way, you use properties like invoker.goals.2 to configure the goals for a second invocation of Maven. Have a look at the example about using Invoker Properties.