void addReturnResult(SSLEngineResult... sslEngineResult) {
      for (SSLEngineResult result : sslEngineResult) {
        returnResults.add(result);
      }
    }
add an engine operation result to be returned by wrap or unwrap. Like Mockito's thenReturn(),
the last return result will repeat forever
geode-core/src/test/java/org/apache/geode/internal/net/NioSslEngineTest.java