OpenStack Testing (Tempest) of an existing cloud
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Tempest Coding Guide

Tempest Specific Commandments

  • [T102] Cannot import OpenStack python clients in tempest/api tests
  • [T104] Scenario tests require a services decorator
  • [T105] Unit tests cannot use setUpClass
  • [T106] vim configuration should not be kept in source files.

Test Data/Configuration

  • Assume nothing about existing test data
  • Tests should be self contained (provide their own data)
  • Clean up test data at the completion of each test
  • Use configuration files for values that will vary by environment

Exception Handling

According to the The Zen of Python the Errors should never pass silently. Tempest usually runs in special environment (jenkins gate jobs), in every error or failure situation we should provide as much error related information as possible, because we usually do not have the chance to investigate the situation after the issue happened.

In every test case the abnormal situations must be very verbosely explained, by the exception and the log.

In most cases the very first issue is the most important information.

Try to avoid using try blocks in the test cases, both the except and finally block could replace the original exception, when the additional operations leads to another exception.

Just letting an exception to propagate, is not bad idea in a test case, at all.

Try to avoid using any exception handling construct which can hide the errors origin.

If you really need to use a try block, please ensure the original exception at least logged. When the exception is logged you usually need to raise the same or a different exception anyway.

Use of self.addCleanup is often a good way to avoid having to catch exceptions and still ensure resources are correctly cleaned up if the test fails part way through.

Use the self.assert* methods provided by the unit test framework the signal failures early.

Avoid using the alone, it's stack trace will signal the line as the origin of the error.

Avoid constructing complex boolean expressions for assertion. The self.assertTrue or self.assertFalse without a msg argument, will just tell you the single boolean value, and you will not know anything about the values used in the formula, the msg argument might be good enough for providing more information.

Most other assert method can include more information by default. For example self.assertIn can include the whole set.

Recommended to use testtools matcher for more tricky assertion. [doc]

You can implement your own specific matcher as well. [doc]

If the test case fails you can see the related logs and the information carried by the exception (exception class, backtrack and exception info). This and the service logs are your only guide to find the root cause of flaky issue.

Test cases are independent

Every test_method must be callable individually and MUST NOT depends on, any other test_method or test_method ordering.

Test cases MAY depend on commonly initialized resources/facilities, like credentials management, testresources and so on. These facilities, MUST be able to work even if just one test_method selected for execution.

Service Tagging

Service tagging is used to specify which services are exercised by a particular test method. You specify the services with the decorator. For example:

@services('compute', 'image')

Valid service tag names are the same as the list of directories in tempest.api that have tests.

For scenario tests having a service tag is required. For the api tests service tags are only needed if the test method makes an api call (either directly or indirectly through another service) that differs from the parent directory name. For example, any test that make an api call to a service other than nova in tempest.api.compute would require a service tag for those services, however they do not need to be tagged as compute.

Negative Tests

When adding negative tests to tempest there are 2 requirements. First the tests must be marked with a negative attribute. For example:

def test_resource_no_uuid(self):

The second requirement is that all negative tests must be added to a negative test file. If such a file doesn't exist for the particular resource being tested a new test file should be added.

Test skips because of Known Bugs

If a test is broken because of a bug it is appropriate to skip the test until bug has been fixed. You should use the skip_because decorator so that Tempest's skip tracking tool can watch the bug status.


def test_this_and_that(self):


  • Do not submit changesets with only testcases which are skipped as they will not be merged.
  • Consistently check the status code of responses in testcases. The earlier a problem is detected the easier it is to debug, especially where there is complicated setup required.

Parallel Test Execution

Tempest by default runs its tests in parallel this creates the possibility for interesting interactions between tests which can cause unexpected failures. Tenant isolation provides protection from most of the potential race conditions between tests outside the same class. But there are still a few of things to watch out for to try to avoid issues when running your tests in parallel.

  • Resources outside of a tenant scope still have the potential to conflict. This is a larger concern for the admin tests since most resources and actions that require admin privileges are outside of tenants.
  • Races between methods in the same class are not a problem because parallelization in tempest is at the test class level, but if there is a json and xml version of the same test class there could still be a race between methods.
  • The rand_name() function from tempest.common.utils.data_utils should be used anywhere a resource is created with a name. Static naming should be avoided to prevent resource conflicts.
  • If the execution of a set of tests is required to be serialized then locking can be used to perform this. See AggregatesAdminTest in tempest.api.compute.admin for an example of using locking.

Stress Tests in Tempest

Any tempest test case can be flagged as a stress test. With this flag it will be automatically discovery and used in the stress test runs. The stress test framework itself is a facility to spawn and control worker processes in order to find race conditions (see tempest/stress/ for more information). Please note that these stress tests can't be used for benchmarking purposes since they don't measure any performance characteristics.


def test_this_and_that(self):

This will flag the test test_this_and_that as a stress test. The parameter class_setup_per gives control when the setUpClass function should be called.

Good candidates for stress tests are:

  • Scenario tests
  • API tests that have a wide focus

Sample Configuration File

The sample config file is autogenerated using a script. If any changes are made to the config variables in tempest then the sample config file must be regenerated. This can be done running the script: tools/

Unit Tests

Unit tests are a separate class of tests in tempest. They verify tempest itself, and thus have a different set of guidelines around them:

  1. They can not require anything running externally. All you should need to run the unit tests is the git tree, python and the dependencies installed. This includes running services, a config file, etc.
  2. The unit tests cannot use setUpClass, instead fixtures and testresources should be used for shared state between tests.