T instance = generator.newFreshProxy(interfaceType);
    new EqualsTester()
        .addEqualityGroup(wrapperFunction.apply(instance), wrapperFunction.apply(instance))
        .addEqualityGroup(wrapperFunction.apply(generator.newFreshProxy(interfaceType)))
        // TODO: add an overload to EqualsTester to print custom error message?
        .testEquals();
  }

        assertTrue(isNotEmpty.apply("test"));
        assertTrue(isNotEmpty.apply("a"));
        assertFalse(isNotEmpty.apply(""));
        assertFalse(isNotEmpty.apply(null));
    }

    public void test_apply_integer() {
        BooleanFunction<Integer> isPositive = n -> n != null && n > 0;

        assertTrue(isPositive.apply(1));
        assertTrue(isPositive.apply(100));
        assertFalse(isPositive.apply(0));

    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    return Collector.of(
        ImmutableMap.Builder<K, V>::new,
        (builder, input) -> builder.put(keyFunction.apply(input), valueFunction.apply(input)),
        ImmutableMap.Builder::combine,
        ImmutableMap.Builder::buildOrThrow);
  }

  static <T extends @Nullable Object, K, V> Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(

    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    return Collector.of(
        ImmutableMap.Builder<K, V>::new,
        (builder, input) -> builder.put(keyFunction.apply(input), valueFunction.apply(input)),
        ImmutableMap.Builder::combine,
        ImmutableMap.Builder::buildOrThrow);
  }

  static <T extends @Nullable Object, K, V> Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(

        }
        refresh();
    }

    /**
     * Adds a bad word to the suggest index.
     *
     * @param badWord The bad word to add.
     * @param apply   true to apply the changes immediately.
     */
    public void addBadWord(final String badWord, final boolean apply) {
        suggester.indexer().addBadWord(badWord, apply);
        refresh();
    }

    /**

          @Override
          public Arithmetic apply(Arithmetic arithmetic) {
            return new ForwardingArithmetic(arithmetic);
          }
        });
    tester.testForwarding(
        ParameterTypesDifferent.class,
        new Function<ParameterTypesDifferent, ParameterTypesDifferent>() {
          @Override
          public ParameterTypesDifferent apply(ParameterTypesDifferent delegate) {

    assertEquals(p1.apply(1.0f), p2.apply(1.0f));
    assertEquals(p1.apply(5.0f), p2.apply(5.0f));
  }

  public void testForPredicate() {
    Function<Object, Boolean> alwaysTrue = Functions.forPredicate(Predicates.alwaysTrue());
    Function<Object, Boolean> alwaysFalse = Functions.forPredicate(Predicates.alwaysFalse());

    assertTrue(alwaysTrue.apply(0));
    assertFalse(alwaysFalse.apply(0));

    }

    open fun request(request: Request) =
      apply {
        this.request = request
      }

    open fun protocol(protocol: Protocol) =
      apply {
        this.protocol = protocol
      }

    open fun code(code: Int) =
      apply {
        this.code = code
      }

    open fun message(message: String) =
      apply {
        this.message = message
      }

    assertFalse(isNumber.apply(null));
  }

  @GwtIncompatible // Predicates.instanceOf
  public void testIsInstanceOf_interface() {
    Predicate<@Nullable Object> isComparable = Predicates.instanceOf(Comparable.class);

    assertTrue(isComparable.apply(1));
    assertTrue(isComparable.apply(2.0f));
    assertTrue(isComparable.apply(""));
    assertFalse(isComparable.apply(null));
  }

    assertEquals(p1.apply(1.0f), p2.apply(1.0f));
    assertEquals(p1.apply(5.0f), p2.apply(5.0f));
  }

  public void testForPredicate() {
    Function<Object, Boolean> alwaysTrue = Functions.forPredicate(Predicates.alwaysTrue());
    Function<Object, Boolean> alwaysFalse = Functions.forPredicate(Predicates.alwaysFalse());

    assertTrue(alwaysTrue.apply(0));
    assertFalse(alwaysFalse.apply(0));