    @Test
    public void letter() throws Exception {

        Lexer lexer = new Lexer("x");
        List<RobotLine> lines = lexer.lex();
        assertEquals(1, lines.size());
        RobotLine line1 = lines.get(0);
        assertThat(line1.lineNo, is(0));
        assertThat(line1.lineCharPos, is(0));
        assertThat(line1.arguments.size(), is(1));
    }