Develop Reference

What does the "Maven Surefire plugin" means when it test your build?

I am working on understanding Maven and I'm learning about building your Java app with it.
So when I do a :
maven package
It does build my jar as expected but I see in the output console that Maven does build tests (it always say that the test a run and there are no failure).
I researched on the web about that and learned that Maven use a plugin called Maven Surefire. But I can't understand what does that plugin do to my code, what does the tests "means" ? What does the tests do with my code and how it works behind the console ?

The Maven surefire plugin runs the tests you have written. These are usually in the src/test/java folder. If you have none, the plugin does nothing.

Is this only one question? :D
So. Different things are going on.
You create an application with Java. To test the single components / packages / classes that you create most people use JUnit or TestNg. You usually have dedicated test classes that verify your production code behaves as intended without you clicking through all the things on every change.
When you now use maven to run your build the pom.xml file defines a packaging - in your case "jar" since you create a jar file. The packaging defines what set of default plugins run in the defined maven phases. You probably recognize package here. Maven executes all phases up to package and the registered / configured plugins.
To execute those tests maven provides the surefire plugin which supports running JUnit or TestNg tests. If you follow the directory conventions your tests reside in src/test/java and the surefire includes naming convention maven will execute those tests in every build (as this is the best practice). If you also want to write integration tests then there is the failsafe plugin. That plugin is not enabled by default and runs in different maven phases.
So the tests just run your production code - in fact they just do what you implement in the tests. They don't alter it in any way.
The maven introduction documentation has step by step explanations: Maven in 5 Minutes and the Getting Started Guide.
Starting from scratch this is probably a lot. So don't rush this. The build setup and test setup are very important things to have.

How to run selenium test cases in jenkins?

I had been introduced to concept of CI lately and was trying to work on jenkins CI. I was stuck up in one thing . How to trigger executable testng files in jenkins CI. For ex locally in our machines we just run testng.xml to execute couple of test cases. In the same way how can we trigger this xml file to run in jenkins CI ?

In most cases with jenkins you wouldn't use an executable. Normally you'd run the wrapper for the tests (Junit/Nunit etc.) which Jenkins is fully capable of running on it's own.

You can use this article to run TestNG tests using Maven:
Running TestNG tests using maven
After configuration is completed just add Invoke top-level Maven targets step to the Build Steps in Jenkins (Maven plugin should be installed). The target should be test in this case.
If you will face with any errors during configuration, try to google them.

If you are not using any build tool like maven or ant, you can invoke it from command line as we'll and specify your suite file. Make sure to set the correct class paths http://testng.org/doc/documentation-main.html#running-testng
You can put this as a build step in Jenkins.
Add a compilation step prior to this step. I haven't ever tried it - have always used ant or maven, but that is where I would start exploring.

How to benchmark the methods inside JUnit test?

I need to identify the slow running methods inside JUnit test class. For example Surefire site report can give me the test methods running time, but how to identify the running time of the methods inside?
I have the following contraption:
Programming language - Java
Build tool - Apache Maven
Test runner - Apache Surefire
Test driver- JUnit
Browser driver - Selenium WebDriver
Artifacts repository - Sonatype Nexus
Continious integration - Jenkins
SCM - Subversion (to be migrated to Git)

Example open source projects built using maven and test with TestNG

I'm looking at adding TestNG support to http://pitest.org and could do with some real and dirty code to try it out on.
Can anyone suggest some smallish open source projects that are build using maven and use TestNG for unit testing?
For clarity - I am not asking how to configure maven to use TestNG, I am looking for some example projects to use as input to a mutation testing tool.

Off the top of my head, Seam and Tapestry both use TestNG. Obviously, TestNG itself uses TestNG.
There is also a lot of activity on the Selenium front, check out the Selenium boards.

Usually you only need to add the testng dependency to your pom with scope test and surefire will handle that already...(may be you need to update surefire plugin).

Run all the junit tests that are in a given package in Netbeans?

We have a bunch junit tests in our current project. Essentially we are looking for a way to run all the test in a given package. Currently in Netbeans I see you can run all the tests or a single test, but no way to run a a sub-set of tests.
Is this built into Netbeans? Or is there another way we can do this?

In JUnit this is achieved through TestSuite. You can check for more information here (look at the code, not at the pictures).
At least in the Eclipse IDE there is a functionality that lets you add a new TestSuite, select which tests it is to include and then have the IDE generate it for you.
I haven't seen such thing in Netbeans, but you should check for any additional JUnit plugins.

Just set up junit test groups like documented e.g. on this question and then run the test group via your ant or maven build.