Diff action is created on the Common Test Runner Side for the TestMethod node by default. If you are not see this action
in the context menu if the test method node it means the method getActions of the TestMethod node was ovverided in the
maven. So, not a JUnit nor Common Test Runner issue.
Reassign to maven for evaluation.

with a sample maven project, I'm able to see the "View difference" menu item on failed tests and I can invoke it and see
the diff.
It seems to work both for "Test" project popup menu (invoked by maven) and with "Test file" action invoked on the test
file (invoked by ant via Compile on Save)

reassigning to dsimonek for deeper evaluation, could be platform dependent, in any case we would need some sample
project and detailed steps to reproduce.

This doesn't show for me in any maven project, big or small using NB 6.7 RC2. 

Created attachment 85187 [details]
sample project that works for me

rdelaplante, please provide more details and exact reproduction steps, I can't reproduce and it seems everything works
OK for me, but I'm not sure if I understand your bug description, please provide more details. I attached small project
with failing test that works OK for me, and the same applies to issue 166142. Thank you.

I verified that it works fine on this tiny project, but it still does not work on larger maven projects.  I just hear my
computer beep when i click the "Go To Source" menu item, and nothing happens.   How do I test?  I change a passing test
to make it fail, save, press CTRL-F6 to run the tests.  I expand the JUnit tree nodes to expose the failing test, right
click on the failing test and click "Go To Source".  I hear my computer beep, and nothing happens.   Maybe try checking
out an open source Maven2 project of a good size and try it.  

Hopefully tonight or this weekend I can create a new Maven2 web project with the same dependencies my current project
has, and reproduce the problem without having to put my closed source code in there.  Maybe the issue is related to my
pom.  For example, I have this in there:

<plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.4.3</version>
                <configuration>
                    <!-- Only execute test cases -->
                    <includes>
                        <include>**/*Test.java</include>
                    </includes>
                    <!-- Exclude individual integration tests since they are
                         executed using a suite. Also exclude the test suite
                         until we can figure out how to get Spring working with
                         multiple data sources in the unit test environment -->
                    <excludes>
                        <exclude>**/*IntegrationTest.java, **/*IntegrationTestSuite.java</exclude>
                    </excludes>
                </configuration>
            </plugin>

rdelaplante, any news on this? I still have no success with reproducing this issue...

Well, I'm now using NB 6.7.1 on OpenSolaris and I still odn't get a diff menu item.  I can see the text pane on the
right says :

Unexpected method call findInstanceByPK("testa"):
    findInstanceByPK("abcd"): expected: at least 1, actual: 0)

But there is no diff context menu on that failed test.  All of the issues I reported with the junit window are still
happening.  I often can't double click a failed test to go to the source, or use the Go To Source cntext menu either
because it does nothing.  Sometimes it works though, so I have no idea what the problem is. 

Still missing enough details to reproduce and evaluate.