protected List<? extends Token> getRemainingBuffer() {
			if ( n==0 ) {
				return Collections.emptyList();
			}

			return Arrays.asList(tokens).subList(p, n);
		}
For testing.  What's in moving window into token stream from
 current index, LT(1) or tokens[p], to end of buffer?
tool-testsuite/test/org/antlr/v4/test/tool/TestUnbufferedTokenStream.java