assertThat(FluentIterable.from(sortedSet).first()).isAbsent();
  }

  public void testFirst_iterable() {
    Set<String> set = ImmutableSet.of("a", "b", "c");
    assertThat(FluentIterable.from(set).first()).hasValue("a");
  }

  public void testFirst_emptyIterable() {
    Set<String> set = newHashSet();
    assertThat(FluentIterable.from(set).first()).isAbsent();
  }

  public void testLast_list() {

      Path dir = fs.getPath("dir");
      Files.createDirectory(dir);

      ByteSource source = MoreFiles.asByteSource(dir);

      assertThat(source.sizeIfKnown()).isAbsent();

      assertThrows(IOException.class, () -> source.size());
    }
  }

  public void testByteSource_size_ofSymlinkToDirectory() throws IOException {

      Path dir = fs.getPath("dir");
      Files.createDirectory(dir);

      ByteSource source = MoreFiles.asByteSource(dir);

      assertThat(source.sizeIfKnown()).isAbsent();

      assertThrows(IOException.class, () -> source.size());
    }
  }

  public void testByteSource_size_ofSymlinkToDirectory() throws IOException {

      Optional<Charset> charset = ((MediaType) field.get(null)).charset();
      if (field.getName().endsWith("_UTF_8")) {
        assertThat(charset).hasValue(UTF_8);
      } else {
        assertThat(charset).isAbsent();
      }
    }
  }

  @J2ktIncompatible
  @GwtIncompatible // reflection
  public void testConstants_areUnique() {
    assertThat(getConstants()).containsNoDuplicates();
  }

  @J2ktIncompatible

    assertNotNull(ArbitraryInstances.get(Joiner.class).join(ImmutableList.of("a")));
    assertNotNull(ArbitraryInstances.get(Splitter.class).split("a,b"));
    assertThat(ArbitraryInstances.get(com.google.common.base.Optional.class)).isAbsent();
    ArbitraryInstances.get(Stopwatch.class).start();
    assertNotNull(ArbitraryInstances.get(Ticker.class));
    assertFreshInstanceReturned(Random.class);
    assertEquals(

    assertThat(tryFind(list, equalTo("pants"))).hasValue("pants");
    assertThat(tryFind(list, Predicates.alwaysTrue())).hasValue("cool");
    assertThat(tryFind(list, Predicates.alwaysFalse())).isAbsent();
    assertCanIterateAgain(list);
  }

  private static class TypeA {}

  private interface TypeB {}

  private static class HasBoth extends TypeA implements TypeB {}