Automatically choose correct barcode function.

Tests for barcode function.

test/test_function_barcode.py

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+#!/usr/bin/python
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import escpos.printer as printer
+from escpos.constants import BARCODE_TYPE_A, BARCODE_TYPE_B
+from escpos.capabilities import Profile, BARCODE_B
+from escpos.exceptions import BarcodeTypeError
+import pytest
+
+
+@pytest.mark.parametrize("bctype,data,expected", [
+    ('EAN13', '4006381333931',
+        b'\x1ba\x01\x1dh@\x1dw\x03\x1df\x00\x1dH\x02\x1dk\x024006381333931\x00')
+])
+def test_barcode(bctype, data, expected):
+    instance = printer.Dummy()
+    instance.barcode(data, bctype)
+    assert instance.output == expected
+
+
+@pytest.mark.parametrize("bctype,supports_b", [
+    ('invalid', True),
+    ('CODE128', False),
+])
+def test_lacks_support(bctype, supports_b):
+    profile = Profile(features={BARCODE_B: supports_b})
+    instance = printer.Dummy(profile=profile)
+    with pytest.raises(BarcodeTypeError):
+        instance.barcode('test', bctype)
+
+    assert instance.output == ''