1 WrapperTest.java

@RunWith(Suite.class)
@Suite.SuiteClasses({
  WrapperTest.DegenerateTests.class,
  WrapperTest.wrapWordsTest.class
})

public class WrapperTest {
  public static class DegenerateTests {
    @Test
    public void emptyString() throws Exception {
      assertThat(wrap("", 1), equalTo(""));
    }

    @Test
    public void stringShorterThanCol() throws Exception {
      assertThat(wrap("this", 10), equalTo("this"));
    }
  }

  public static class wrapWordsTest {
    @Test
    public void wrapTwoWordsAfterSpace() throws Exception {
      assertThat(wrap("word word", 6), equalTo("word\nword"));
    }

    @Test
    public void wrapThreeWordsAfterFirstSpace() throws Exception {
      assertThat(wrap("word word word", 6), equalTo("word\nword\nword"));  
    }
  }
}

2 Wrapper.java

public class Wrapper {
  public static String wrap(String s, int col) {
   if (s.length() <= col)
     return s;
    else
     return s.replaceAll(" ", "\n");
  }
}