[MIG] document_page_approval: Migration to 9.0

* Lint error corrected
* test improved
* lint error corrected in test file
* readme corrected
* test improved
* test of document page history workflow added
* CI error corrected
* dreipst comment
* Migration to new api improved in model's file and data tag remove in xml file
* code totally migrate to odoo 9.0 api
* test bug fixed
* test error fixed
* Lint error improved

document_page_approval/tests/test_document_page_approval.py

@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+from openerp.tests import common
+
+
+class TestDocumentPageApproval(common.TransactionCase):
+    """Test document page approval model."""
+
+    def test_get_display_content(self):
+        """Test page display content."""
+        # Check content of a category
+        category = self.env['document.page'].search([
+            ('name', '=', 'OpenERP Features')
+        ])
+
+        self.assertIsNotNone(category.display_content, 'a category')
+
+        # Check content of a page
+        pages = self.env['document.page'].search([
+            ('parent_id', '=', category.id)
+        ])
+        page = pages[0]
+        self.assertIsNotNone(page.display_content, 'Page content')
+
+        # Check if approval is required
+        self.assertTrue(page.is_approval_required(page) ==
+                        category.approval_required)
+
+        # Check content of an approval page
+        page.approval_required = True
+
+        self.assertIsNotNone(page.display_content, 'Page content')
+
+        # Check if approval is required
+        self.assertTrue(page.is_approval_required(page))
+
+        # Check if parent approval is required
+        self.assertTrue(page.is_parent_approval_required)