assertSame(canonical, internerFunction.apply(not));
  }

  public void testNullPointerExceptions() {
    new NullPointerTester().testAllPublicStaticMethods(Interners.class);
  }

  public void testConcurrencyLevel_zero() {
    Interners.InternerBuilder builder = Interners.newBuilder();
    assertThrows(IllegalArgumentException.class, () -> builder.concurrencyLevel(0));
  }

  public void testConcurrencyLevel_negative() {

    assertSame(canonical, internerFunction.apply(not));
  }

  public void testNullPointerExceptions() {
    new NullPointerTester().testAllPublicStaticMethods(Interners.class);
  }

  public void testConcurrencyLevel_zero() {
    Interners.InternerBuilder builder = Interners.newBuilder();
    assertThrows(IllegalArgumentException.class, () -> builder.concurrencyLevel(0));
  }

  public void testConcurrencyLevel_negative() {

    CacheBuilder.newBuilder().initialCapacity(Integer.MAX_VALUE);
    // that the builder didn't blow up is enough;
    // don't actually create this monster!
  }

  public void testConcurrencyLevel_zero() {
    CacheBuilder<Object, Object> builder = CacheBuilder.newBuilder();
    assertThrows(IllegalArgumentException.class, () -> builder.concurrencyLevel(0));
  }

  public void testConcurrencyLevel_setTwice() {