Maven plugin invoker integration tests

[dflemstr]

I saw that there was a system-tests folder that was not being used by anything in the build/CI process of this plugin. So I converted those tests into proper Maven integration tests by using the maven-invoker-plugin. Roughly what this adds is that now when you run mvn verify or mvn install in this repo, you get a part like this:

[INFO] --- maven-invoker-plugin:1.9:integration-test (integration-test) @ missinglink-maven-plugin ---
[INFO] Building: 00-test-harness/pom.xml
[INFO] [INFO] Scanning for projects...
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] [INFO] Reactor Build Order:
[INFO] [INFO] 
[INFO] [INFO] parent
[INFO] [INFO] a
[INFO] [INFO] a
[INFO] [INFO] a-class-duplicate
[INFO] [INFO] b
[INFO] [INFO]                                                                         
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] [INFO] Building parent 1-SNAPSHOT
[INFO] [INFO] ------------------------------------------------------------------------

... (building the test harness) ...

[INFO] [INFO] Reactor Summary:
[INFO] [INFO] 
[INFO] [INFO] parent ............................................. SUCCESS [  3.789 s]
[INFO] [INFO] a .................................................. SUCCESS [  5.555 s]
[INFO] [INFO] a .................................................. SUCCESS [  0.208 s]
[INFO] [INFO] a-class-duplicate .................................. SUCCESS [  0.152 s]
[INFO] [INFO] b .................................................. SUCCESS [  0.196 s]
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] [INFO] BUILD SUCCESS
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] [INFO] Total time: 10.104 s
[INFO] [INFO] Finished at: 2015-07-19T15:55:22+02:00
[INFO] [INFO] Final Memory: 21M/211M
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] ..SUCCESS (14.0 s)
[INFO] Building: class-missing/pom.xml
[INFO] [INFO] Scanning for projects...
[INFO] [INFO]                                                                         
[INFO] [INFO] ------------------------------------------------------------------------
[INFO] [INFO] Building class-missing 1-SNAPSHOT
[INFO] [INFO] ------------------------------------------------------------------------

... (building each integration test project in turn) ...

[INFO] [INFO] ------------------------------------------------------------------------
[INFO] ..SUCCESS (19.4 s)
[INFO] 
[INFO] --- maven-invoker-plugin:1.9:verify (integration-test) @ missinglink-maven-plugin ---
[INFO] -------------------------------------------------
[INFO] Build Summary:
[INFO]   Passed: 10, Failed: 0, Errors: 0, Skipped: 0
[INFO] -------------------------------------------------

Interesting stuff that could be done on top of this:

• I added support for having verification scripts in each integration test project. You can add a verify.groovy (for example) next to the pom.xml of any of the tests and that groovy file can verify certain things from the output. This might be useful if the missinglink plugin outputs some kind of structured report; you can assert that a class duplicate was found or something.
• There can be negative tests where the plugin is allowed to fail the build.

[dflemstr]

@pettermahlen @mattnworb @spkrka

[dflemstr]

(Unrelated, I also converted version numbers from 0.x-SNAPSHOT to x-SNAPSHOT and removed redundant <packaging>jar</packaging> to save trees)

[pettermahlen]

Looks great! This is what I wanted to do with the system tests, only better. :)

I only wonder why coveralls reports decreased coverage for the CheckMojo, that doesn't make sense to me. But I'm thinking that looks like some sort of bug rather than something cause by this PR.

[mattnworb]

This is great - thank you @dflemstr :raised_hands: