add server test for GetMap with styles and opacities

Covers https://issues.qgis.org/issues/15553 case

tests/src/python/test_qgsserver_wms_getmap.py

@@ -811,6 +811,25 @@ class TestQgsServerWMSGetMap(QgsServerTestBase):
         r, h = self._result(self._execute_request(qs))
         self._img_diff_error(r, h, "WMS_GetMap_Opacities2")
 
+        # Test OPACITIES with specific STYLES
+        qs = "?" + "&".join(["%s=%s" % i for i in list({
+            "MAP": urllib.parse.quote(self.projectPath),
+            "SERVICE": "WMS",
+            "VERSION": "1.1.1",
+            "REQUEST": "GetMap",
+            "LAYERS": "Country,Hello,dem",
+            "STYLES": "origin,default,default",
+            "FORMAT": "image/png",
+            "BBOX": "-16817707,-4710778,5696513,14587125",
+            "HEIGHT": "500",
+            "WIDTH": "500",
+            "CRS": "EPSG:3857",
+            "OPACITIES": "125,50,150"
+        }.items())])
+
+        r, h = self._result(self._execute_request(qs))
+        self._img_diff_error(r, h, "WMS_GetMap_Opacities3")
+
     def test_wms_getmap_highlight(self):
         # highlight layer with color separated from sld
         qs = "?" + "&".join(["%s=%s" % i for i in list({