Add test for color button that setting color to transparent

will retain non-alpha color components

(cherry-picked from 4089cc5)

tests/src/python/CMakeLists.txt

@@ -14,6 +14,7 @@ ADD_PYTHON_TEST(PyQgsAttributeTableModel test_qgsattributetablemodel.py)
 #ADD_PYTHON_TEST(PyQgsAuthenticationSystem test_qgsauthsystem.py)
 ADD_PYTHON_TEST(PyQgsBlendModes test_qgsblendmodes.py)
 ADD_PYTHON_TEST(PyQgsCategorizedSymbolRendererV2 test_qgscategorizedsymbolrendererv2.py)
+ADD_PYTHON_TEST(PyQgsColorButtonV2 test_qgscolorbuttonv2.py)
 ADD_PYTHON_TEST(PyQgsColorScheme test_qgscolorscheme.py)
 ADD_PYTHON_TEST(PyQgsColorSchemeRegistry test_qgscolorschemeregistry.py)
 ADD_PYTHON_TEST(PyQgsComposerEffects test_qgscomposereffects.py)

tests/src/python/test_qgscolorbuttonv2.py

@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsColorButtonV2.
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+__author__ = 'Nyall Dawson'
+__date__ = '25/05/2016'
+__copyright__ = 'Copyright 2016, The QGIS Project'
+# This will get replaced with a git SHA1 when you do a git archive
+__revision__ = '$Format:%H$'
+
+import qgis  # NOQA
+
+from qgis.gui import QgsColorButtonV2
+from qgis.testing import start_app, unittest
+from qgis.PyQt.QtGui import QColor
+start_app()
+
+
+class TestQgsColorButtonV2(unittest.TestCase):
+
+    def testClearingColors(self):
+        """
+        Test setting colors to transparent
+        """
+
+        # start with a valid color
+        button = QgsColorButtonV2()
+        button.setAllowAlpha(True)
+        button.setColor(QColor(255, 100, 200, 255))
+        self.assertEqual(button.color(), QColor(255, 100, 200, 255))
+
+        # now set to no color
+        button.setToNoColor()
+        # ensure that only the alpha channel has changed - not the other color components
+        self.assertEqual(button.color(), QColor(255, 100, 200, 0))
+
+
+if __name__ == '__main__':
+    unittest.main()