@Test public void testBufferWrapSize2() throws Exception {
   		CharStream input = createStream("01234", 2);
        assertEquals('0', input.LA(1));
        input.consume();
        assertEquals('1', input.LA(1));
        input.consume();
        assertEquals('2', input.LA(1));
        input.consume();
        assertEquals('3', input.LA(1));
        input.consume();
        assertEquals('4', input.LA(1));
        input.consume();
   		assertEquals(IntStream.EOF, input.LA(1));
   	}
It is not valid to pass a mark to {@link IntStream#seek}, but
{@link UnbufferedCharStream} creates marks in such a way that this
invalid usage results in an {@link IllegalArgumentException}.
tool-testsuite/test/org/antlr/v4/test/tool/TestUnbufferedCharStream.java