Update text() test to use dummy printer.

test/Dies ist ein Test.LF.txt

@@ -1 +0,0 @@
-Dies ist ein Test.

test/test_function_text.py

@@ -12,38 +12,14 @@ 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
 from escpos.printer import Dummy
-import os
-
-import filecmp
-
-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_text_dies_ist_ein_test_lf():
     """test the text printing function with simple string and compare output"""
-    instance = printer.File(devfile=devfile)
+    instance = Dummy()
     instance.text('Dies ist ein Test.\n')
-    instance.flush()
-    assert(filecmp.cmp('test/Dies ist ein Test.LF.txt', devfile))
+    assert instance.output == 'Dies ist ein Test.\n'
 
 
 def test_block_text():