improve the exceptions

also adds a stump for the tests for MagicEncode

test/test_magicencode.py

@@ -0,0 +1,54 @@
+#!/usr/bin/python
+"""tests for panel button function
+
+:author: `Patrick Kanzler <patrick.kanzler@fablab.fau.de>`_
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2016 `python-escpos <https://github.com/python-escpos>`_
+:license: GNU GPL v3
+"""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+from nose.tools import with_setup
+
+import escpos.printer as printer
+import os
+
+devfile = 'testfile'
+
+
+def setup_testfile():
+    """create a testfile as devfile"""
+    fhandle = open(devfile, 'a')
+    try:
+        os.utime(devfile, None)
+    finally:
+        fhandle.close()
+
+
+def teardown_testfile():
+    """destroy testfile again"""
+    os.remove(devfile)
+
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_panel_button_on():
+    """test the panel button function (enabling) by comparing output"""
+    instance = printer.File(devfile=devfile)
+    instance.panel_buttons()
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1B\x63\x35\x00')
+
+
+@with_setup(setup_testfile, teardown_testfile)
+def test_function_panel_button_off():
+    """test the panel button function (disabling) by comparing output"""
+    instance = printer.File(devfile=devfile)
+    instance.panel_buttons(False)
+    instance.flush()
+    with open(devfile, "rb") as f:
+        assert(f.read() == b'\x1B\x63\x35\x01')