new_contents: #!/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')
      
      
      
subject: add a test demostrating modifying a layer which was originally loaded via xml and is later modified in python