Running tests via nosestests fails due to insufficient test isolation

A failure looks like this:

  ......................SSSSS...............................................................................................................................................................................F
  ======================================================================
  FAIL: test_instance_level_keys_replace_project_level_keys (tests.unittests.test_datasource.test_gce.TestDataSourceGCE)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/home/lars/src/cloud-init/tests/unittests/test_datasource/test_gce.py", line 150, in test_instance_level_keys_replace_project_level_keys
      self.assertEqual([key_content], self.ds.get_public_ssh_keys())
  AssertionError: Lists differ: ['ssh-rsa JustAUser root@server'] != ['ssh-rsa AA2..+aRD0fyVw== root@server']

  First differing element 0:
  ssh-rsa JustAUser root@server
  ssh-rsa AA2..+aRD0fyVw== root@server

  - ['ssh-rsa JustAUser root@server']
  + ['ssh-rsa AA2..+aRD0fyVw== root@server']
  -------------------- >> begin captured logging << --------------------
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/id' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/id', 'allow_redirects': True, 'method': 'GET', 'headers': {'X-Google-Metadata-Request': 'True', 'User-Agent': 'Cloud-Init/0.7.9'}} configuration
  requests.packages.urllib3.connectionpool: INFO: Starting new HTTP connection (1): metadata.google.internal
  requests.packages.urllib3.connectionpool: DEBUG: "GET /computeMetadata/v1/instance/id HTTP/1.1" 200 3
  cloudinit.url_helper: DEBUG: Read from http://metadata.google.internal/computeMetadata/v1/instance/id (200, 3b) after 1 attempts
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/zone' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/zone', 'allow_redirects': True, 'method': 'GET', 'headers': {'X-Google-Metadata-Request': 'True', 'User-Agent': 'Cloud-Init/0.7.9'}} configuration
  requests.packages.urllib3.connectionpool: INFO: Starting new HTTP connection (1): metadata.google.internal
  requests.packages.urllib3.connectionpool: DEBUG: "GET /computeMetadata/v1/instance/zone HTTP/1.1" 200 7
  cloudinit.url_helper: DEBUG: Read from http://metadata.google.internal/computeMetadata/v1/instance/zone (200, 7b) after 1 attempts
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/hostname' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/hostname', 'allow_redirects': True, 'method': 'GET', 'headers': {'X-Google-Metadata-Request': 'True', 'User-Agent': 'Cloud-Init/0.7.9'}} configuration
  requests.packages.urllib3.connectionpool: INFO: Starting new HTTP connection (1): metadata.google.internal
  requests.packages.urllib3.connectionpool: DEBUG: "GET /computeMetadata/v1/instance/hostname HTTP/1.1" 200 24
  cloudinit.url_helper: DEBUG: Read from http://metadata.google.internal/computeMetadata/v1/instance/hostname (200, 24b) after 1 attempts
  cloudinit.url_helper: DEBUG:...

I've opened an upstream issue
https://github.com/gabrielfalcao/HTTPretty/issues/316

I'm pretty sure that is the root of why you see it in your case and we do not when running in tox.

This bug is believed to be fixed in cloud-init in 17.1. If this is still a problem for you, please make a comment and set the state back to New

Thank you.

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2793