fix file-printer did not flush

The file-printer did not automatically flush and thus behaved
differently to the other printer-classes.
Now the default behaviour is to flush after every call of _raw(). This
can be disabled by calling the file-printer with auto_flush=False.

fixes #106

src/escpos/printer.py

@@ -229,13 +229,15 @@ class File(Escpos):
 
     """
 
-    def __init__(self, devfile="/dev/usb/lp0", *args, **kwargs):
+    def __init__(self, devfile="/dev/usb/lp0", auto_flush=True, *args, **kwargs):
         """
 
         :param devfile : Device file under dev filesystem
+        :param auto_flush: automatically call flush after every call of _raw()
         """
         Escpos.__init__(self, *args, **kwargs)
         self.devfile = devfile
+        self.auto_flush = auto_flush
         self.open()
 
     def open(self):
@@ -256,6 +258,8 @@ class File(Escpos):
         :type msg: bytes
         """
         self.device.write(msg)
+        if self.auto_flush:
+            self.flush()
 
     def close(self):
         """ Close system file """

test/test_printer_file.py

@@ -0,0 +1,70 @@
+#!/usr/bin/python
+#  -*- coding: utf-8 -*-
+"""tests for the File printer
+
+: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
+
+import six
+
+import mock
+from hypothesis import given
+from hypothesis.strategies import text
+
+import escpos.printer as printer
+
+if six.PY3:
+    mock_open_call = 'builtins.open'
+else:
+    mock_open_call = '__builtin__.open'
+
+@given(path=text())
+@mock.patch(mock_open_call)
+@mock.patch('escpos.escpos.Escpos.__init__')
+def test_load_file_printer(mock_escpos, mock_open, path):
+    """test the loading of the file-printer"""
+    printer.File(devfile=path)
+    assert mock_escpos.called
+    mock_open.assert_called_with(path, "wb")
+
+
+@given(txt=text())
+@mock.patch.object(printer.File, 'device')
+@mock.patch(mock_open_call)
+@mock.patch('escpos.escpos.Escpos.__init__')
+def test_auto_flush(mock_escpos, mock_open, mock_device, txt):
+    """test auto_flush in file-printer"""
+    p = printer.File(auto_flush=False)
+    # inject the mocked device-object
+    p.device = mock_device
+    p._raw(txt)
+    assert not mock_device.flush.called
+    mock_device.reset_mock()
+    p = printer.File(auto_flush=True)
+    # inject the mocked device-object
+    p.device = mock_device
+    p._raw(txt)
+    assert mock_device.flush.called
+
+
+@given(txt=text())
+@mock.patch.object(printer.File, 'device')
+@mock.patch(mock_open_call)
+def test_flush_on_close(mock_open, mock_device, txt):
+    """test flush on close in file-printer"""
+    p = printer.File(auto_flush=False)
+    # inject the mocked device-object
+    p.device = mock_device
+    p._raw(txt)
+    assert not mock_device.flush.called
+    p.close()
+    assert mock_device.flush.called
+    assert mock_device.close.called