Added test at the service level, to see how well madeleine copes with errors. Looks like it does cope with them.

app/models/page.rb

@@ -15,6 +15,7 @@ class Page
   end
 
   def revise(content, created_at, author)
+
     if not @revisions.empty? and content == @revisions.last.content
       raise Instiki::ValidationError.new(
           "You have tried to save page '#{name}' without changing its content")

test/unit/wiki_service_test.rb

@@ -37,27 +37,66 @@ class WikiServiceTest < Test::Unit::TestCase
         'state of any object, and therefore should not be logged by Madeleine!', 
         Time.now, 'AlexeyVerkhovsky'
 
-    assert_doesnt_change_state :authenticate, 'pswd'
+    assert_doesnt_change_state_or_log :authenticate, 'pswd'
-    assert_doesnt_change_state :read_page, 'instiki', 'TestReadOnlyOperations'
+    assert_doesnt_change_state_or_log :read_page, 'instiki', 'TestReadOnlyOperations'
-    assert_doesnt_change_state :setup?
+    assert_doesnt_change_state_or_log :setup?
-    assert_doesnt_change_state :webs
+    assert_doesnt_change_state_or_log :webs
     
     @s.write_page 'instiki', 'FirstPage', "Electric shocks, I love 'em", 
         Time.now, 'DavidHeinemeierHansson'
     assert_equal "Electric shocks, I love 'em", @s.read_page('instiki', 'FirstPage').content
   end
 
+  def test_aborted_transaction
+    @s.write_page 'instiki', 'FirstPage', "Electric shocks, I love 'em", 
+        10.minutes.ago, 'DavidHeinemeierHansson'
 
-  def assert_doesnt_change_state(method, *args)
+    assert_doesnt_change_state('revise_page with unchanged content') {
+      begin
+        @s.revise_page 'instiki', 'FirstPage', "Electric shocks, I love 'em", 
+            Time.now, 'DavidHeinemeierHansson'
+        fail 'Expected Instiki::ValidationError not raised'
+      rescue Instiki::ValidationError
+      end
+    }
+  end
+
+
+  # Checks that a method call or a block doesn;t change the persisted state of the wiki
+  # Usage:
+  #   assert_doesnt_change_state :read_page, 'instiki', 'TestReadOnlyOperations'
+  # or
+  #   assert_doesnt_change_state {|wiki| wiki.webs}
+
+  def assert_doesnt_change_state(method, *args, &block)
+    _assert_doesnt_change_state(including_command_log = false, method, *args, &block)
+  end
+  
+  # Same as assert_doesnt_change_state, but also asserts that no vommand log is generated
+  def assert_doesnt_change_state_or_log(method, *args, &block)
+    _assert_doesnt_change_state(including_command_log = true, method, *args, &block)
+  end
+
+  private
+
+  def _assert_doesnt_change_state(including_log, method, *args)
     WikiService.snapshot
     last_snapshot_before = File.read(Dir[RAILS_ROOT + 'storage/test/*.snapshot'].last)
 
-    @s.send(method, *args)
+    if block_given?
+      yield @s
+    else
+      @s.send(method, *args)
+    end
+
+    if including_log
+      command_logs = Dir[RAILS_ROOT + 'storage/test/*.command_log']
+      assert command_logs.empty?, "Calls to #{method} should not be logged"
+    end
 
-    command_logs = Dir[RAILS_ROOT + 'storage/test/*.command_log']
-    assert command_logs.empty?, "Calls to #{method} should not be logged"
     last_snapshot_after = File.read(Dir[RAILS_ROOT + 'storage/test/*.snapshot'].last)
     assert last_snapshot_before == last_snapshot_after,
-      'Calls to #{method} should not change the state of any persisted object' 
+        'Calls to #{method} should not change the state of any persisted object' 
   end
+
 end