Tests for PreconditionFailed error messages.

Change to relation.rb to bring element selection in-line with that of way, so to return nil to be caught later, rather than raise an error.
Change to way.rb to clarify which way on diff upload.

test/functional/changeset_controller_test.rb

@@ -397,6 +397,7 @@ EOF
     post :upload, :id => 2
     assert_response :precondition_failed, 
       "shouldn't be able to upload a invalid deletion diff: #{@response.body}"
+    assert_equal "Precondition failed: Way 3 still used by relation 1.", @response.body
 
     # check that nothing was, in fact, deleted
     assert_equal true, Node.find(current_nodes(:node_used_by_relationship).id).visible

test/functional/node_controller_test.rb

@@ -197,12 +197,14 @@ class NodeControllerTest < ActionController::TestCase
     delete :delete, :id => current_nodes(:used_node_1).id
     assert_response :precondition_failed,
        "shouldn't be able to delete a node used in a way (#{@response.body})"
+    assert_equal "Precondition failed: Node 3 is still used by way 1.", @response.body
 
     # in a relation...
     content(nodes(:node_used_by_relationship).to_xml)
     delete :delete, :id => current_nodes(:node_used_by_relationship).id
     assert_response :precondition_failed,
        "shouldn't be able to delete a node used in a relation (#{@response.body})"
+    assert_equal "Precondition failed: Node 5 is still used by relation 3.", @response.body
   end
 
   ##

test/functional/relation_controller_test.rb

@@ -341,6 +341,7 @@ class RelationControllerTest < ActionController::TestCase
     # expect failure
     assert_response :precondition_failed, 
         "relation upload with invalid node did not return 'precondition failed'"
+    assert_equal "Precondition failed: Cannot create relation: data or member data is invalid.", @response.body
   end
 
   # -------------------------------------
@@ -465,6 +466,7 @@ class RelationControllerTest < ActionController::TestCase
     delete :delete, :id => current_relations(:public_used_relation).id
     assert_response :precondition_failed, 
        "shouldn't be able to delete a relation used in a relation (#{@response.body})"
+    assert_equal "Precondition failed: The relation 5 is used in relation 6.", @response.body
 
     # this should work when we provide the appropriate payload...
     content(relations(:multi_tag_relation).to_xml)

test/functional/way_controller_test.rb

@@ -164,6 +164,7 @@ class WayControllerTest < ActionController::TestCase
     # expect failure
     assert_response :precondition_failed, 
         "way upload with invalid node did not return 'precondition failed'"
+    assert_equal "Precondition failed: Way  requires the node with id 0, which either does not exist, or is not visible.", @response.body
 
     # create a way with no nodes
     content "<osm><way changeset='#{open_changeset_id}'>" +
@@ -172,6 +173,7 @@ class WayControllerTest < ActionController::TestCase
     # expect failure
     assert_response :precondition_failed, 
         "way upload with no node did not return 'precondition failed'"
+    assert_equal "Precondition failed: Cannot create way: data is invalid.", @response.body
 
     # create a way inside a closed changeset
     content "<osm><way changeset='#{closed_changeset_id}'>" +
@@ -286,6 +288,7 @@ class WayControllerTest < ActionController::TestCase
     delete :delete, :id => current_ways(:used_way).id
     assert_response :precondition_failed, 
        "shouldn't be able to delete a way used in a relation (#{@response.body})"
+    assert_equal "Precondition failed: Way 3 still used by relation 1.", @response.body
 
     # this won't work since the way never existed
     delete :delete, :id => 0