private static final String TEST_STRING =
      "\0abyz\u0080\u0100\u0800\u1000ABYZ\uffff" + SMALLEST_SURROGATE + "0189" + LARGEST_SURROGATE;

  // Escapes nothing
  private static final UnicodeEscaper NOP_ESCAPER =
      new UnicodeEscaper() {
        @Override
        protected char @Nullable [] escape(int c) {
          return null;
        }
      };

  // Escapes everything except [a-zA-Z0-9]

    runConcurrentlyMutatedTest(elements(), ops(add(1), nop()), wrap);

    runConcurrentlyMutatedTest(elements(), ops(add(1), remove()), wrap);

    runConcurrentlyMutatedTest(elements(), ops(nop(), add(1)), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), nop()), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), add(2)), wrap);

  private static final String TEST_STRING =
      "\0abyz\u0080\u0100\u0800\u1000ABYZ\uffff" + SMALLEST_SURROGATE + "0189" + LARGEST_SURROGATE;

  // Escapes nothing
  private static final UnicodeEscaper NOP_ESCAPER =
      new UnicodeEscaper() {
        @Override
        protected char @Nullable [] escape(int c) {
          return null;
        }
      };

  // Escapes everything except [a-zA-Z0-9]

    runConcurrentlyMutatedTest(elements(), ops(add(1), nop()), wrap);

    runConcurrentlyMutatedTest(elements(), ops(add(1), remove()), wrap);

    runConcurrentlyMutatedTest(elements(), ops(nop(), add(1)), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), nop()), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), add(2)), wrap);