String canonical = "a";
    String not = new String("a");

    Interner<String> pool = Interners.newWeakInterner();
    assertSame(canonical, pool.intern(canonical));
    assertSame(canonical, pool.intern(not));
  }

  public void testWeak_null() {
    Interner<String> pool = Interners.newWeakInterner();
    assertThrows(NullPointerException.class, () -> pool.intern(null));
  }

  public void testWeak_builder() {

    String canonical = "a";
    String not = new String("a");

    Interner<String> pool = Interners.newWeakInterner();
    assertSame(canonical, pool.intern(canonical));
    assertSame(canonical, pool.intern(not));
  }

  public void testWeak_null() {
    Interner<String> pool = Interners.newWeakInterner();
    assertThrows(NullPointerException.class, () -> pool.intern(null));
  }

  public void testWeak_builder() {

  }

  public enum InternerImpl implements InternerImplEnum {
    WeakInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {
        Interner<E> interner = Interners.newWeakInterner();
        for (E e : contents) {
          E unused = interner.intern(e);
        }
        return interner;
      }
    },
    StrongInternerImpl {
      @Override

  }

  public enum InternerImpl implements InternerImplEnum {
    WeakInternerImpl {
      @Override
      public <E> Interner<E> create(Collection<E> contents) {
        Interner<E> interner = Interners.newWeakInterner();
        for (E e : contents) {
          E unused = interner.intern(e);
        }
        return interner;
      }
    },
    StrongInternerImpl {
      @Override