Start with the following file:

import org.junit.runner.RunWith
import org.scalatest.junit.JUnitRunner

@RunWith(classOf[JUnitRunner])
class TestFoo {

}

Hit Ctrl-Shift-O for organise imports. Result:

import org.junit.runner.RunWith

@RunWith(classOf[JUnitRunner])
class TestFoo {

}

This now fails to compile as it does not know what JUnitRunner is.