[FIX+IMP] base_user_role: Several things:

* FIX: Update users' groups when a role is deleted
* IMP: add some test cases to check user's groups when its last role line is removed
* FIX: ensure that the user's groups are updated when its last role line is removed

base_user_role/models/role.py

@@ -46,6 +46,13 @@ class ResUsersRole(models.Model):
         self.update_users()
         return res
 
+    @api.multi
+    def unlink(self):
+        users = self.mapped('user_ids')
+        res = super(ResUsersRole, self).unlink()
+        users.set_groups_from_roles(force=True)
+        return res
+
     @api.multi
     def update_users(self):
         """Update all the users concerned by the roles identified by `ids`."""
@@ -91,5 +98,5 @@ class ResUsersRoleLine(models.Model):
     def unlink(self):
         users = self.mapped('user_id')
         res = super(ResUsersRoleLine, self).unlink()
-        users.set_groups_from_roles()
+        users.set_groups_from_roles(force=True)
         return res

base_user_role/models/user.py

@@ -32,12 +32,13 @@ class ResUsers(models.Model):
         return res
 
     @api.multi
-    def set_groups_from_roles(self):
+    def set_groups_from_roles(self, force=False):
         """Set (replace) the groups following the roles defined on users.
-        If no role is defined on the user, its groups are let untouched.
+        If no role is defined on the user, its groups are let untouched unless
+        the `force` parameter is `True`.
         """
         for user in self:
-            if not user.role_line_ids:
+            if not user.role_line_ids and not force:
                 continue
             group_ids = []
             role_lines = user.role_line_ids.filtered(