[IMP] tests: make post_install the default

content/developer/reference/backend/testing.rst

@@ -58,19 +58,6 @@ related to testing Odoo content (modules, mainly):
 
 .. autofunction:: odoo.tests.tagged
 
-By default, tests are run once right after the corresponding module has been
-installed. Test cases can also be configured to run after all modules have
-been installed, and not run right after the module installation::
-
-  # coding: utf-8
-  from odoo.tests import HttpCase, tagged
-
-  # This test should only be executed after all modules have been installed.
-  @tagged('-at_install', 'post_install')
-  class WebsiteVisitorTests(HttpCase):
-    def test_create_visitor_on_tracked_page(self):
-        Page = self.env['website.page']
-
 The most common situation is to use
 :class:`~odoo.tests.TransactionCase` and test a property of a model
 in each method::
@@ -190,7 +177,7 @@ they're not going to get run:
     import unittest
     from odoo.tests import tagged
 
-    @tagged('standard', 'at_install')
+    @tagged('standard', 'post_install')
     class SmallTest(unittest.TestCase):
         ...
 
@@ -234,15 +221,19 @@ Special tags
   :option:`--test-tags <odoo-bin --test-tags>` also defaults to ``standard``.
 
   That means untagged test will be executed by default when tests are enabled.
-- ``at_install``: Means that the test will be executed right after the module
-  installation and before other modules are installed. This is a default
-  implicit tag.
+
 - ``post_install``: Means that the test will be executed after all the modules
-  are installed. This is what you want for HttpCase tests most of the time.
+  are installed. This is a default implicit tag.
+
+- ``at_install``: Means that the test will be executed right after the module
+  installation and before other modules are installed.
+
+  This should be used seldomly as it prevents test runs from being parallelized
+  on runbot. A valuable addition is a comment above to test to explain why it
+  needs to be run before other modules are installed.
 
-  Note that this is *not exclusive* with ``at_install``, however since you
-  will generally not want both ``post_install`` is usually paired with
-  ``-at_install`` when tagging a test class.
+  Note that this is *exclusive* with ``post_install`` so ``at_install`` is
+  usually paired with ``-post_install`` when tagging a test class.
 
 Examples
 ~~~~~~~~

content/developer/tutorials/unit_tests.rst

@@ -48,7 +48,7 @@ Before knowing how to write tests, we need to know how to run them.
                         specifies if we want to include or exclude tests
                         matching this spec. The tag will match tags added on a
                         class with a @tagged decorator (all Test classes have
-                        'standard' and 'at_install' tags until explicitly
+                        'standard' and 'post_install' tags until explicitly
                         removed, see the decorator documentation). '*' will
                         match all tags. If tag is omitted on include mode, its
                         value is 'standard'. If tag is omitted on exclude
@@ -175,17 +175,16 @@ coming from modules your module doesn't depend on.
 
 .. code-block:: python
 
-  from odoo.tests.common import TransactionCase
-  from odoo.tests import tagged
+  from odoo.tests import tagged, TransactionCase
 
   # The CI will run these tests after all the modules are installed,
   # not right after installing the one defining it.
-  @tagged('post_install', '-at_install')  # add `post_install` and remove `at_install`
+  @tagged('post_install')  # this is the default
   class PostInstallTestCase(TransactionCase):
       def test_01(self):
           ...
 
-  @tagged('at_install')  # this is the default
+  @tagged('at_install', '-post_install')  # add `at_install` and remove `post_install`
   class AtInstallTestCase(TransactionCase):
       def test_01(self):
           ...
@@ -241,13 +240,12 @@ These test classes are built on top of the ``unittest`` python module.
 
 .. code-block:: python
 
-  from odoo.tests.common import TransactionCase
+  from odoo.tests import TransactionCase
   from odoo.exceptions import UserError
-  from odoo.tests import tagged
+
 
   # The CI will run these tests after all the modules are installed,
   # not right after installing the one defining it.
-  @tagged('post_install', '-at_install')
   class EstateTestCase(TransactionCase):
 
       @classmethod