Eclipse/Maven: JUnit tests not compiled when running them

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I am working on a project using Maven and Eclipse (m2eclipse plugin). I've got problems with the JUnit tests:

Sometimes, when running them within Eclipse, they wont be compiled, but the old class files are used instead. When I delete the class files, I get ClassNotFoundExceptions in Eclipse. I then have to manually recompile them by using mvn test-compile or other goals.

I also noticed that the class files of the tests sometimes are put into the classes subdirectory instead of test-classes.

I really can't figure out what is wrong.

The JUnit java files are within src/main/java and are correctly named (*Test.java).

Do I have to compile and run them always via Maven? Why doesn't Eclipse compile the files when I want to run them? (Interestingly, sometimes it does. Sometimes everything works perfectly.)

Best Solution

I had the same problem with STS Eclipse (Spring development variant), m2e and JUnit. The solution was to set the output folder for src/test/java to target/test-classes:

  1. Right click the src/test/java folder in the Package Explorer
  2. Select Build Path -> Configure Output Folder
  3. Enter target/test-classes, click OK

Now the changes in test classes are compiled correctly and you should be able to run JUnit tests in Eclipse.

The problem is that Eclipse compiles the unit tests to the default output folder target/classes while JUnit plugin correctly tries to run them from test-classes.

There are a few duplicates to this question: