assertThat(cache.asMap().values()).contains(value2);
      assertEquals(ImmutableSet.of(immutableEntry(key2, value2)), cache.asMap().entrySet());
    }
  }

  // fails in Maven with 64-bit JDK: https://github.com/google/guava/issues/1568

  // A simple type whose .toString() will return the same value each time, but without maintaining
  // a strong reference to that value.
  static class Key {

    Throwable thrownReflectionFailure = null;
    try {
      helper = new SafeAtomicHelper();
    } catch (Throwable reflectionFailure) { // sneaky checked exception
      // Some Android 5.0.x Samsung devices have bugs in JDK reflection APIs that cause
      // getDeclaredField to throw a NoSuchFieldException when the field is definitely there.
      // For these users fallback to a suboptimal implementation, based on synchronized. This will

    return new SingletonImmutableSet<>(e1);
  }

  /*
   * TODO: b/315526394 - Skip the Builder entirely for the of(...) methods, since we don't need to
   * worry that we might trigger the fallback to the JDK-backed implementation? (The varargs one
   * _could_, so we could keep it as it is. Or we could convince ourselves that hash flooding is
   * unlikely in practice there, too.)
   */

  /**

      try {
        // 1.8, 9, 10, 11, 12 etc
        val version = jvmVersion.toInt()
        if (version >= 9) return null
      } catch (_: NumberFormatException) {
        // expected on >= JDK 9
      }

      // Find Jetty's ALPN extension for OpenJDK.
      try {
        val alpnClassName = "org.eclipse.jetty.alpn.ALPN"
        val alpnClass = Class.forName(alpnClassName, true, null)

  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {
    NullPointerTester tester = new NullPointerTester();
    // Necessary until JDK15:
    // https://bugs.openjdk.org/browse/JDK-8202469
    tester.ignore(Equivalence.class.getMethod("wrap", Object.class));

    tester.testAllPublicStaticMethods(Equivalence.class);
    tester.testAllPublicInstanceMethods(Equivalence.equals());

  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {
    NullPointerTester tester = new NullPointerTester();
    // Necessary until JDK15:
    // https://bugs.openjdk.org/browse/JDK-8202469
    tester.ignore(Equivalence.class.getMethod("wrap", Object.class));

    tester.testAllPublicStaticMethods(Equivalence.class);
    tester.testAllPublicInstanceMethods(Equivalence.equals());

        Long.MIN_VALUE,
        Long.MAX_VALUE
      };

  private static final double[] VALUES = Doubles.concat(NUMBERS, new double[] {NaN});

  // We need to test that our method behaves like the JDK method.
  @SuppressWarnings("InlineMeInliner")
  public void testHashCode() {
    for (double value : VALUES) {
      assertThat(Doubles.hashCode(value)).isEqualTo(Double.hashCode(value));
    }
  }

    // TODO(lukes): assert that the logs are full of errors
  }

  /**
   * Runs the corresponding {@link FuturesTest} test method in a new classloader that disallows
   * certain core JDK classes.
   */
  private void runTestMethod(ClassLoader classLoader) throws Exception {
    ClassLoader oldClassLoader = Thread.currentThread().getContextClassLoader();

  private static final int GREATEST = Integer.MAX_VALUE;

  private static final int[] VALUES = {LEAST, (int) -1, (int) 0, (int) 1, GREATEST};

  // We need to test that our method behaves like the JDK method.
  @SuppressWarnings("InlineMeInliner")
  public void testHashCode() {
    for (int value : VALUES) {
      assertThat(Ints.hashCode(value)).isEqualTo(Integer.hashCode(value));
    }
  }

   * properties, including:
   *
   * <ul>
   *   <li>{@code java.vendor.version} (added in Java 11, listed as optional as of Java 13)
   *   <li>{@code jdk.module.*} (added in Java 9, optional)
   * </ul>
   */
  public @Nullable String value() {
    return System.getProperty(key);
  }

  /** Returns a string representation of this system property. */