Return result of current_user_can for create_post.
Change logic to use the request object directly to determine params set.
Return error if post_type would be changed in update_item method.

Includes tests.
Remove duplicate setting of the id parameter in update item tests.
Add test for invalid id during update.
Add return after dispatch in test methods to normalize whitespace.
Change wp_update_post and wp_insert_post to return WP_Error.
Add tests for creating posts with passwords.
Add post password check to response check.
Trim new line after check of post response.
Add tests for creating pages with post parent.
Consistent naming for permission error tests.
Add test for creating a post with invalid id.
Add test to create a private post without permission.