This question is tangentially related to How can I create JUnit stub methods in eclipse? but it doesn\'t answer my specific question.
Assuming you have an existing JUnit
The usual working cycle with unit tests is to create the test case first
public void test_new_method() {
ClassUnderTest x = new ClassUnderTest();
x.NewMethod();
}
At that point Eclipse will give you a warning that the method "NewMethod" does not exist. Than you simply select a "Quick Fix" (Ctrl-1 or Ctrl-2 i'm not sure) to create the missing method in the class.