code: public final ExpectBuilder withEchoInput(Appendable firstInput, Appendable... otherInputs) {
          this.echoInput = firstInput;
          this.echoInputs = otherInputs;
          return this;
      }
docs: Enables printing of all the received data. Useful for debugging to monitor I/O activity.
  Optional, by default is unset.
  <p/>
  If the only {@code firstInput} is specified then the data received from all the inputs is
  echoed to it.
  <p/>
  The build method throws an {@link java.lang.IllegalArgumentException} if the number of the
  {@code otherInputs}
  parameters does not correspond to the number of the input streams. That is,
  if {@code otherInputs}
  is specified, the number of them must be equal to the number of inputs minus 1.
  <p/>
  The byte data received from the input streams is converted to strings using the
  builder's charset. See {@link ExpectBuilder#withCharset(java.nio.charset.Charset)} for
  more information.
  
  @param firstInput  where to echo the received data for the first input. If {@code
  otherInputs} are empty, then
  all the data will be echoed to it.
  @param otherInputs where to echo the received data for other inputs.
  @return this