def METHOD_NAME(self):
    # Simulates a multi-instance test
    component = "foo"
    orig_contents1 = "bar = 42"
    orig_contents2 = "bar = 17"
    contents_to_append = "baz = 101"
    # Setup
    filename1 = self.write_user_nl_file(component, orig_contents1, suffix="_0001")
    filename2 = self.write_user_nl_file(component, orig_contents2, suffix="_0002")
    # Exercise
    user_nl_utils.append_to_user_nl_files(
        caseroot=self._caseroot, component=component, contents=contents_to_append
    )
    # Verify
    expected_contents1 = orig_contents1 + "\n" + contents_to_append + "\n"
    expected_contents2 = orig_contents2 + "\n" + contents_to_append + "\n"
    self.assertFileContentsEqual(
        expected_contents1, os.path.join(self._caseroot, filename1)
    )
    self.assertFileContentsEqual(
        expected_contents2, os.path.join(self._caseroot, filename2)
    )