public InternerBuilder strong() {
      this.strong = true;
      return this;
    }

    /**
     * Instructs the {@link InternerBuilder} to build a weak interner.
     *
     * @see Interners#newWeakInterner()
     */
    @CanIgnoreReturnValue
    @GwtIncompatible // java.lang.ref.WeakReference
    public InternerBuilder weak() {
      this.strong = false;
      return this;
    }

    /**

    public InternerBuilder strong() {
      this.strong = true;
      return this;
    }

    /**
     * Instructs the {@link InternerBuilder} to build a weak interner.
     *
     * @see Interners#newWeakInterner()
     */
    @CanIgnoreReturnValue
    @GwtIncompatible // java.lang.ref.WeakReference
    public InternerBuilder weak() {
      this.strong = false;
      return this;
    }

    /**

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

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

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

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

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

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