def test_do_assemble_outputs_disassembly(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble('c000 lda #$ab')

        out = stdout.getvalue()
        self.assertEqual("$c000  a9 ab     LDA #$ab\n", out)

 def test_do_add_label_syntax_error(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon.do_add_label('should be label space value')
     out = stdout.getvalue()
     err = "Syntax error: should be label space value\n"
     self.assertTrue(out.startswith(err))

 def test_tilde_shortcut_without_space_for_vice_compatibility(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon.onecmd('~$10')
     out = stdout.getvalue()
     expected = "+16\n$10\n0020\n00010000\n"
     self.assertTrue(out.startswith(expected))

    def test_shortcut_for_registers(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_help('r')

        out = stdout.getvalue()
        self.assertTrue(out.startswith('registers'))

 def test_registers_updates_single_register(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon.do_registers('x=42')
     out = stdout.getvalue()
     self.assertEqual("", out)
     self.assertEqual(0x42, mon._mpu.x)

    def test_shortcut_for_mem(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_help('m')

        out = stdout.getvalue()
        self.assertTrue(out.startswith('mem <address_range>'))

 def test_do_add_breakpoint_adds_number(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon.do_add_breakpoint('ffd2')
     out = stdout.getvalue()
     self.assertTrue(out.startswith("Breakpoint 0 added at $FFD2"))
     self.assertTrue(0xffd2 in mon._breakpoints)

    def test_help_assemble(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.help_assemble()

        out = stdout.getvalue()
        self.assertTrue("assemble <address>" in out)

    def test_help_cd(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.help_cd()

        out = stdout.getvalue()
        self.assertTrue(out.startswith("cd <directory>"))

    def test_do_assemble_passes_addr_for_relative_branch_calc(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble('4000 bvs $4005')

        out = stdout.getvalue()
        self.assertEqual("$4000  70 03     BVS $4005\n", out)

    def test_do_assemble_constrains_address_to_valid_range(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble("-1 lda #$ab")

        out = stdout.getvalue()
        self.assertEqual("Overflow error: -1 lda #$ab\n", out)

    def test_do_assemble_shows_overflow_error(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble('c000 lda #$fff')

        out = stdout.getvalue()
        self.assertEqual("Overflow error: c000 lda #$fff\n", out)

    def test_do_assemble_shows_bad_syntax_error(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble('c000 foo')

        out = stdout.getvalue()
        self.assertEqual("Syntax error: foo\n", out)

    def test_do_assemble_shows_bad_label_error(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_assemble('nonexistant rts')

        out = stdout.getvalue()
        self.assertEqual("Bad label: nonexistant rts\n", out)

 def test_goto_without_breakpoints_stops_execution_at_brk(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon._breakpoints = []
     mon._mpu.memory = [ 0xEA, 0xEA, 0x00, 0xEA ]
     mon.do_goto('0')
     self.assertEqual(0x02, mon._mpu.pc)

    def test_do_cd_with_no_dir_shows_help(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_cd("")

        out = stdout.getvalue()
        self.assertTrue(out.startswith("cd <directory>"))

 def test_show_breakpoints_ignores_deleted_breakpoints(self):
     stdout = StringIO()
     mon = Monitor(stdout=stdout)
     mon._breakpoints = [None, 0xffd2]
     mon.do_show_breakpoints('')
     out = stdout.getvalue()
     self.assertTrue(out.startswith("Breakpoint 1: $FFD2"))

    def test_do_cd_with_bad_dir_shows_error(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_cd("/path/to/a/nonexistant/directory")

        out = stdout.getvalue()
        self.assertTrue(out.startswith("Cannot change directory"))

    def test_do_mem_shows_help_when_given_extra_args(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.do_mem('c000 c001')

        out = stdout.getvalue()
        self.assertTrue(out.startswith('mem <address_range>'))

    def test_help_cycles(self):
        stdout = StringIO()
        mon = Monitor(stdout=stdout)
        mon.help_cycles()

        out = stdout.getvalue()
        self.assertTrue(out.startswith("Display the total number of cycles"))