This is a test suite to make sure that editing of objects works as expected:

Import the user's name and password:

  >>> from Products.PloneTestCase.PloneTestCase import default_user
  >>> from Products.PloneTestCase.PloneTestCase import default_password

Get the portal and the home paths:

  >>> portal_path = '/'.join(self.portal.getPhysicalPath())
  >>> folder_path = '/'.join(self.folder.getPhysicalPath())

Let's create a page to play with:

  >>> folder.invokeFactory('Document', 'test-page', title='My Title')
  'test-page'

Let's edit our test page, but leave off some required fields:

  >>> edit_path = folder_path + '/test-page/atct_edit'
  >>> print http(r"""
  ... POST %s HTTP/1.1
  ... Authorization: Basic %s:%s
  ... Content-Type: multipart/form-data; boundary=---------------------------6981500387474556631359179914
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="id"
  ...
  ... test-page
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="title"
  ...
  ...
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="description"
  ...
  ...
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="description_text_format"
  ...
  ... text/plain
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="text"
  ...
  ... <p>a</p>
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="allowDiscussion"
  ...
  ... None
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="fieldset"
  ...
  ... default
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="form.submitted"
  ...
  ... 1
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="form_submit"
  ...
  ... Save
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="text_text_format"
  ...
  ... text/html
  ... -----------------------------6981500387474556631359179914--
  ... """ % (edit_path, default_user, default_password),
  ...        handle_errors=False)
  HTTP/1.1 200 OK...
  <h1 class="documentFirstHeading"> Edit ...Page... </h1>...
  <div class="field error ArchetypesStringWidget"...
  <div>Title is required, please correct.</div>
  <input...type="text"...name="title"...value="My Title".../>...
  <input...type="submit"...name="form_submit"...value="Save".../>...

No changes should have been made:
  >>> obj = folder['test-page']
  >>> obj.Title()
  'My Title'
  >>> obj.Description()
  ''
  >>> obj.getText()
  ''

And let's edit it properly:

  >>> print http(r"""
  ... POST %s HTTP/1.1
  ... Authorization: Basic %s:%s
  ... Content-Type: multipart/form-data; boundary=---------------------------6981500387474556631359179914
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="id"
  ...
  ... test-page
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="title"
  ...
  ... My Title 2
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="description"
  ...
  ... A description
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="description_text_format"
  ...
  ... text/plain
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="text"
  ...
  ... <p>a</p>
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="allowDiscussion"
  ...
  ... None
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="fieldset"
  ...
  ... default
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="form.submitted"
  ...
  ... 1
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="form_submit"
  ...
  ... Save
  ... -----------------------------6981500387474556631359179914
  ... Content-Disposition: form-data; name="text_text_format"
  ...
  ... text/html
  ... -----------------------------6981500387474556631359179914--
  ... """ % (edit_path, default_user, default_password),
  ...        handle_errors=False)
  HTTP/1.1 302 Moved Temporarily
  ...
  Location: ...test-page?portal_status_message=Changes%20saved.

Let's make sure our changes were applied:

  >>> obj = folder['test-page']
  >>> obj.Title()
  'My Title 2'
  >>> obj.getText().strip()
  '<p>a</p>'