[processing] Add test, help for create spatial index alg

Author: nyalldawson

python/plugins/processing/algs/help/qgis.yaml

@@ -114,6 +114,9 @@ qgis:createpointsalonglines: >
 
   Start and end points can be defined, so the first and last point do not fall on the line first and last node. Start and end points are defined as distances, mesaureed from the first and last nodes of the lines, in the units of the projection used by the lines layer.
 
+qgis:createspatialindex: >
+  Creates an index to speed up access to the features in a layer based on their spatial location. Support for spatial index creation is dependent on the layer's data provider.
+
 qgis:delaunaytriangulation: >
   This algorithm creates a polygon layer with the delaunay triangulation corresponding to a  points layer.
 

python/plugins/processing/algs/qgis/SpatialIndex.py

@@ -62,7 +62,7 @@ def processAlgorithm(self, progress):
 
         if provider.capabilities() & QgsVectorDataProvider.CreateSpatialIndex:
             if not provider.createSpatialIndex():
-                progress.setInfo(self.tr('Can not create spatial index'))
+                progress.setInfo(self.tr('Could not create spatial index'))
         else:
             progress.setInfo(self.tr("Layer's data provider does not support "
                                      "spatial indexes"))

python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

@@ -2104,3 +2104,17 @@ tests:
         name: expected/create_attr_index_points.shp
         type: vector
         in_place_result: true
+
+  - algorithm: qgis:createspatialindex
+    name: Create spatial index
+    params:
+      INPUT:
+        name: custom/points.shp
+        type: vector
+        in_place: true
+    results:
+      INPUT:
+        name: expected/create_attr_index_points.shp
+        type: vector
+        in_place_result: true
+