assertThat(Primitives.isWrapperType(void.class)).isFalse();
  }

  public void testWrap() {
    assertThat(Primitives.wrap(int.class)).isSameInstanceAs(Integer.class);
    assertThat(Primitives.wrap(Integer.class)).isSameInstanceAs(Integer.class);
    assertThat(Primitives.wrap(String.class)).isSameInstanceAs(String.class);
  }

  public void testUnwrap() {
    assertThat(Primitives.unwrap(Integer.class)).isSameInstanceAs(int.class);

    assertThat(Primitives.isWrapperType(void.class)).isFalse();
  }

  public void testWrap() {
    assertThat(Primitives.wrap(int.class)).isSameInstanceAs(Integer.class);
    assertThat(Primitives.wrap(Integer.class)).isSameInstanceAs(Integer.class);
    assertThat(Primitives.wrap(String.class)).isSameInstanceAs(String.class);
  }

  public void testUnwrap() {
    assertThat(Primitives.unwrap(Integer.class)).isSameInstanceAs(int.class);

      return input.length();
    }
  }

  private static final Equivalence<String> LENGTH_EQUIVALENCE =
      Equivalence.equals().onResultOf(LengthFunction.INSTANCE);

  public void testWrap() {
    new EqualsTester()
        .addEqualityGroup(
            LENGTH_EQUIVALENCE.wrap("hello"),
            LENGTH_EQUIVALENCE.wrap("hello"),
            LENGTH_EQUIVALENCE.wrap("world"))