When Compile-on-Save is enabled on Maven-based NetBeans module projects, the Compile-on-Save system normally picks up changes in any module on which the platform application depends. This also works when executing a class with a main method--I can change source files in any module on which the module containing the main class depends, and when I run the main class again, the changes are incorporated into the newly executed build. However, when running JUnit tests, only changes in the module containing the test seem to be taken into account.

To reproduce (the way I just did it on NetBeans 8.0):
* Create a new Maven-based NetBeans Platform project, and add two new modules (let's call them ModuleA and ModuleB). Make sure Compile-on-Save is enabled.
* In ModuleA, create a class with a single static method that returns a string "Foo1", say SomeClass.getFoo(). Make the package containing it a public package.
* Have ModuleB depend on ModuleA.
* In ModuleA, create a class MainClass with a main method in it, and a JUnit test class TestClass with a JUnit test method in it. Do a "System.out.println(SomeClass.getFoo())" from both of them.
* Clean and build.
* Run MainClass; it should print "Foo1". Test the TestClass; it should also print "Foo1".
* Now change "Foo1" to "Foo2" in ModuleA.
* Run MainClass again; it will correctly print "Foo2".
* Test TestClass again; it will now, incorrectly, still print "Foo1". Only once ModuleA is built manually will the JUnit test print "Foo2". Note that changes to TestClass itself, or any other class in ModuleB, will still correctly be picked up by Compile-on-Save when running the JUnit test in ModuleB.

(Compile-on-Save with Maven-based NetBeans Module projects has worked really great for me in the past year, by the way. It's a really invaluable feature.)