add implementation of GS v 0, GS ( L and GS *.

- ported test cases for EscposImage class, copied over 1px and 2px test images from escpos-php
- added test cases over image print function
- updated QR tests to also include image output check
- updated CLI to match new image function options

test/test_image.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+""" Image tests- Check that images from different source formats are correctly
+converted to ESC/POS column & raster formats.
+
+:author: `Michael Billington <michael.billington@gmail.com>`_
+:organization: `python-escpos <https://github.com/python-escpos>`_
+:copyright: Copyright (c) 2016 `Michael Billington <michael.billington@gmail.com>`_
+:license: GNU GPL v3
+"""
+
+from escpos.image import EscposImage
+
+def test_image_black():
+    """
+    Test rendering solid black image
+    """
+    for img_format in ['png', 'jpg', 'gif']:
+        _load_and_check_img('canvas_black.' + img_format, 1, 1, b'\x80', [b'\x80'])
+
+def test_image_black_transparent():
+    """
+    Test rendering black/transparent image
+    """
+    for img_format in ['png', 'gif']:
+        _load_and_check_img('black_transparent.' + img_format, 2, 2, b'\xc0\x00', [b'\x80\x80'])
+
+def test_image_black_white():
+    """
+    Test rendering black/white image
+    """
+    for img_format in ['png', 'jpg', 'gif']:
+        _load_and_check_img('black_white.' + img_format, 2, 2, b'\xc0\x00', [b'\x80\x80'])
+
+def test_image_white():
+    """
+    Test rendering solid white image
+    """
+    for img_format in ['png', 'jpg', 'gif']:
+        _load_and_check_img('canvas_white.' + img_format, 1, 1, b'\x00', [b'\x00'])
+
+def _load_and_check_img(filename, width_expected, height_expected, raster_format_expected, column_format_expected):
+    """
+    Load an image, and test whether raster & column formatted output, sizes, etc match expectations.
+    """
+    im = EscposImage('test/resources/' +  filename)
+    assert(im.width == width_expected)
+    assert(im.height == height_expected)
+    assert(im.to_raster_format() == raster_format_expected)
+    i = 0 
+    for row in im.to_column_format(False):
+        assert(row == column_format_expected[i])
+        i = i + 1