### Question:
PlainTextPrinter implements Printer { @Override public void printErr(String text) { printOut(text); } PlainTextPrinter(Appendable out); @Override void printOut(String text); @Override void printErr(String text); @Override void printMetaIncrement(String text); @Override void printMetaLine(String line);  }### Answer:
@Test public void prints_stderr() { printer.printErr("foo"); printer.printErr("bar"); assertThat(output.toString(), is("foobar")); }