Fix import errors in tests

Author: maribedran

qrcode/tests/test_qrcode_pypng.py

@@ -1,13 +1,16 @@
 import io
 from unittest import mock
 
-import png
+import pytest
+
 
 import qrcode
 import qrcode.util
 from qrcode.image.pure import PyPNGImage
 from qrcode.tests.consts import UNICODE_TEXT
 
+png = pytest.importorskip("png", reason="png is not installed")
+
 
 def test_render_pypng():
     qr = qrcode.QRCode()

qrcode/tests/test_script.py

@@ -48,6 +48,7 @@ def test_stdin_py3_unicodedecodeerror():
 
 
 def test_optimize():
+    pytest.importorskip("PyPNG", reason="Requires PyPNG")
     main("testtext --optimize 0".split())