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: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/project/attributes/sshKeys' with {'url': 'http://metadata.google.internal/computeMetadata/v1/project/attributes/sshKeys', '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/project/attributes/sshKeys HTTP/1.1" 200 41
  cloudinit.url_helper: DEBUG: Read from http://metadata.google.internal/computeMetadata/v1/project/attributes/sshKeys (200, 41b) after 1 attempts
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/sshKeys' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/sshKeys', '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/attributes/sshKeys HTTP/1.1" 404 0
  cloudinit.sources.DataSourceGCE: DEBUG: url instance/attributes/sshKeys raised exception 404 Client Error: Not Found for url: http://metadata.google.internal/computeMetadata/v1/instance/attributes/sshKeys
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data', '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/attributes/user-data HTTP/1.1" 200 14
  cloudinit.url_helper: DEBUG: Read from http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data (200, 14b) after 1 attempts
  cloudinit.url_helper: DEBUG: [0/1] open 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data-encoding' with {'url': 'http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data-encoding', '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/attributes/user-data-encoding HTTP/1.1" 404 0
  cloudinit.sources.DataSourceGCE: DEBUG: url instance/attributes/user-data-encoding raised exception 404 Client Error: Not Found for url: http://metadata.google.internal/computeMetadata/v1/instance/attributes/user-data-encoding
  --------------------- >> end captured logging << ---------------------
  
  ----------------------------------------------------------------------
  Ran 203 tests in 0.856s
  
  FAILED (SKIP=5, failures=1)