So here's my findings:

With https://github.com/openstack/python-tempestconf/commit/ca51d4d94c7b87444c65eb33734ee76e74834188 we added support to microversions and so, tempest started to have compute.min_microversion and compute.max_microversion option in tempest.conf.
With these two options, the test tempest test_auto_allocate_network started to run. This test tries to create 3 servers, and auto allocate networks for that, failing with this:

Traceback (most recent call last):                                                                                                                                                                                                                                                                                             
  File "/usr/lib/python2.7/site-packages/tempest/api/compute/admin/test_auto_allocate_network.py", line 177, in test_server_multi_create_auto_allocate                                                                                                                                                                         
    min_count=3)                                                                                                                                                                                                                                                                                                               
  File "/usr/lib/python2.7/site-packages/tempest/common/compute.py", line 198, in create_test_server                                                                                                                                                                                                                           
    **kwargs)                                                                                                                                                                                                                                                                                                                  
  File "/usr/lib/python2.7/site-packages/tempest/lib/services/compute/servers_client.py", line 97, in create_server                                                                                                                                                                                                            
    resp, body = self.post('servers', post_body)                                                                                                                                                                                                                                                                               
  File "/usr/lib/python2.7/site-packages/tempest/lib/common/rest_client.py", line 283, in post                                                                                                                                                                                                                                 
    return self.request('POST', url, extra_headers, headers, body, chunked)                                                                                                                                                                                                                                                    
  File "/usr/lib/python2.7/site-packages/tempest/lib/services/compute/base_compute_client.py", line 48, in request                                                                                                                                                                                                             
    method, url, extra_headers, headers, body, chunked)                                                                                                                                                                                                                                                                        
  File "/usr/lib/python2.7/site-packages/tempest/lib/common/rest_client.py", line 679, in request                                                                                                                                                                                                                              
    self._error_checker(resp, resp_body)                                                                                                                                                                                                                                                                                       
  File "/usr/lib/python2.7/site-packages/tempest/lib/common/rest_client.py", line 790, in _error_checker                                                                                                                                                                                                                       
    raise exceptions.BadRequest(resp_body, resp=resp)                                                                                                                                                                                                                                                                          
tempest.lib.exceptions.BadRequest: Bad request                                                                                                                                                                                                                                                                                 
Details: {u'message': u'Unable to automatically allocate a network for project 5dbbfe79176e475f9d02c346b3dc03fc', u'code': 400} 

Checking the documentation in [1] in order to have the "Get me a network" behavior, required to execute this test, you need to have a shared pool, and the default network and router configured.

In that case, I went and create a subnet pool with the following command:

# set the public network as default

openstack network set public --default

# Create the subnet pool
openstack subnet pool create --share --default --pool-prefix 10.0.0.0/24 --default-prefix-length 26 shared-default 

Then I got this error:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/tempest/api/compute/admin/test_auto_allocate_network.py", line 177, in test_server_multi_create_auto_allocate
    min_count=3)
  File "/usr/lib/python2.7/site-packages/tempest/common/compute.py", line 253, in create_test_server
    for server in servers:
  File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 220, in __exit__
    self.force_reraise()
  File "/usr/lib/python2.7/site-packages/oslo_utils/excutils.py", line 196, in force_reraise
    six.reraise(self.type_, self.value, self.tb)
  File "/usr/lib/python2.7/site-packages/tempest/common/compute.py", line 236, in create_test_server
    clients.servers_client, server['id'], wait_until)
  File "/usr/lib/python2.7/site-packages/tempest/common/waiters.py", line 76, in wait_for_server_status
    server_id=server_id)
tempest.exceptions.BuildErrorException: Server 2b0cf5c8-1707-461d-8836-2730be4cf3bd failed to build and is in ERROR status
Details: {u'message': u'Exceeded maximum number of retries. Exhausted all hosts available for retrying build failures for instance 2b0cf5c8-1707-461d-8836-2730be4cf3bd.', u'code': 500, u'created': u'2019-04-04T10:34:37Z'}


I believe this is because there aren't enough resources to create 3 vm's.

Now, I am not an neutron specialist here, so my suggestion is one of the bellow:

1 - Keep the test in the skip list
2 - Contact someone who understand about network, to show us how to really configure the subnet pool properly based on our network configuration

I also want to point, this test wasn't being executed before.

Here's how validate-tempest create the public network to execute the tests:

openstack network create public --external \
              --provider-network-type flat \
              --provider-physical-network datacentre

openstack network set datacentre --default

openstack subnet create ext-subnet \
    --allocation-pool \
      start=10.0.0.100,end=10.0.0.120 \
    --no-dhcp \
    --gateway 10.0.0.1 \
    --network public \
    --subnet-range 10.0.0.0/24


I believe we must set a way to link the subnet pool with the ext-subnet, but I don't know how. I check the documentation, but I wasn't able to find it.

1 - https://docs.openstack.org/neutron/rocky/admin/config-auto-allocation.html