add a test demostrating modifying a layer which was originally loaded via xml and is later modified in python

tests/python_tests/layer_modification_test.py

@@ -0,0 +1,63 @@
+#!/usr/bin/env python
+
+from nose.tools import *
+
+import mapnik2
+
+def test_adding_datasource_to_layer():
+    map_string = '''<?xml version="1.0" encoding="utf-8"?>
+<Map>
+
+    <Layer name="world_borders">
+        <StyleName>world_borders_style</StyleName>
+        <StyleName>point_style</StyleName>
+        <!-- leave datasource empty -->
+        <!--
+        <Datasource>
+            <Parameter name="file">../data/shp/world_merc.shp</Parameter>
+            <Parameter name="type">shape</Parameter>
+        </Datasource>
+        -->
+    </Layer>
+
+</Map>
+'''
+    m = mapnik2.Map(256, 256)
+    
+    mapnik2.load_map_from_string(m, map_string)
+    
+    # validate it loaded fine
+    eq_(m.layers[0].styles[0],'world_borders_style')
+    eq_(m.layers[0].styles[1],'point_style')
+    eq_(len(m.layers),1)
+    
+    # also assign a variable reference to that layer
+    # below we will test that this variable references
+    # the same object that is attached to the map
+    lyr = m.layers[0]
+
+    # ensure that there was no datasource for the layer...
+    eq_(m.layers[0].datasource,None)
+    eq_(lyr.datasource,None)
+    
+    # also note that since the srs was black it defaulted to wgs84
+    eq_(m.layers[0].srs,'+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs')
+    eq_(lyr.srs,'+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs')
+    
+    # now add a datasource one...
+    ds = mapnik2.Shapefile(file='../data/shp/world_merc.shp')
+    m.layers[0].datasource = ds
+    
+    # now ensure it is attached
+    eq_(m.layers[0].datasource.name(),"shape")
+    eq_(lyr.datasource.name(),"shape")
+    
+    # and since we have now added a shapefile in spherical mercator, adjust the projection
+    lyr.srs = '+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs'
+    
+    # test that assignment
+    eq_(m.layers[0].srs,'+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
+    eq_(lyr.srs,'+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs')
+    
+    
+