[unit tests] Fix blend modes test

 * Switched to QgsMultiRenderChecker and added control images for precise
 * Add a minimal color tolerance for slight render inconsistencies

tests/src/core/testqgsblendmodes.cpp

@@ -30,7 +30,7 @@
 #include <qgsmultibandcolorrenderer.h>
 #include <qgsrasterlayer.h>
 //qgis test includes
-#include "qgsrenderchecker.h"
+#include "qgsmultirenderchecker.h"
 
 /** \ingroup UnitTests
  * This is a unit test for layer blend modes
@@ -214,10 +214,11 @@ bool TestQgsBlendModes::imageCheck( QString theTestType )
 {
   //use the QgsRenderChecker test utility class to
   //ensure the rendered output matches our control image
-  QgsRenderChecker myChecker;
+  QgsMultiRenderChecker myChecker;
   myChecker.setControlName( "expected_" + theTestType );
   myChecker.setMapSettings( mMapSettings );
-  bool myResultFlag = myChecker.runTest( theTestType, 1500 );
+  myChecker.setColorTolerance( 1 );
+  bool myResultFlag = myChecker.runTest( theTestType );
   mReport += myChecker.report();
   return myResultFlag;
 }

tests/src/python/test_qgsblendmodes.py

@@ -34,7 +34,7 @@
                        QgsMapLayerRegistry,
                        QgsMapRenderer,
                        QgsCoordinateReferenceSystem,
-                       QgsRenderChecker,
+                       QgsMultiRenderChecker,
                        QgsRasterLayer,
                        QgsRasterDataProvider,
                        QgsMultiBandColorRenderer,
@@ -112,9 +112,10 @@ def testVectorBlending(self):
         self.mLineLayer.setBlendMode(QPainter.CompositionMode_Difference)
         self.mPolygonLayer.setBlendMode(QPainter.CompositionMode_Difference)
 
-        checker = QgsRenderChecker()
+        checker = QgsMultiRenderChecker()
         checker.setControlName("expected_vector_blendmodes")
         checker.setMapSettings(self.mapSettings)
+        checker.setColorTolerance( 1 )
 
         myResult = checker.runTest("vector_blendmodes", 1500);
         myMessage = ('vector blending failed')
@@ -137,9 +138,10 @@ def testVectorFeatureBlending(self):
         #Set feature blending for line layer
         self.mLineLayer.setFeatureBlendMode(QPainter.CompositionMode_Plus)
 
-        checker = QgsRenderChecker()
+        checker = QgsMultiRenderChecker()
         checker.setControlName("expected_vector_featureblendmodes")
         checker.setMapSettings(self.mapSettings)
+        checker.setColorTolerance( 1 )
 
         myResult = checker.runTest("vector_featureblendmodes", 1500);
         myMessage = ('vector feature blending failed')
@@ -161,9 +163,10 @@ def testVectorLayerTransparency(self):
         #Set feature blending for line layer
         self.mLineLayer.setLayerTransparency( 50 )
 
-        checker = QgsRenderChecker()
+        checker = QgsMultiRenderChecker()
         checker.setControlName("expected_vector_layertransparency")
         checker.setMapSettings(self.mapSettings)
+        checker.setColorTolerance( 1 )
 
         myResult = checker.runTest("vector_layertransparency", 1500);
         myMessage = ('vector layer transparency failed')
@@ -180,9 +183,11 @@ def testRasterBlending(self):
 
         #Set blending mode for top layer
         self.mRasterLayer1.setBlendMode(QPainter.CompositionMode_Plus)
-        checker = QgsRenderChecker()
+        checker = QgsMultiRenderChecker()
         checker.setControlName("expected_raster_blendmodes")
         checker.setMapSettings(self.mapSettings)
+        checker.setColorTolerance( 1 )
+        checker.setColorTolerance( 1 )
 
         myResult = checker.runTest("raster_blendmodes", 1500);
         myMessage = ('raster blending failed')