processCalled--; // don't count the tail invocation (makes tests a bit more understandable)
    }

    // ensures that the number of invocations looks sane
    void assertInvariants(int expectedBytes) {
      // we should have seen as many bytes as the next multiple of chunk after expectedBytes - 1
      assertEquals(out.toByteArray().length, ceilToMultiple(expectedBytes, chunkSize));

      processCalled--; // don't count the tail invocation (makes tests a bit more understandable)
    }

    // ensures that the number of invocations looks sane
    void assertInvariants(int expectedBytes) {
      // we should have seen as many bytes as the next multiple of chunk after expectedBytes - 1
      assertEquals(out.toByteArray().length, ceilToMultiple(expectedBytes, chunkSize));