The overarching goal of conformance tests is to exercise core Kubernetes functionality in (as much as possible) a provider-agnostic way.
Conformance tests are promoted from existing e2e tests which have been proven to be stable and "non-flaky".
Please read the "Writing good e2e tests" guide as a supplement to this document.
In addition to the "Writing good e2e tests" guide, there are specific requirements that all Conformance tests must adhere to. You can find the definitive list of requirements in the SIG-Arch community docs.
Generally speaking, tests should not target internal behaviors, but instead target exposed system behaviors. Care must also be taken to ensure that the tests do not implicitly test features that are not already subject to conformance. If a feature is needed for a test, make sure that an existing test already covers that feature directly.
When looking for an existing e2e test which exercises a behaviour which is useful for Conformance, you may find that the test does not meet all of the requirements. In these cases, you might either modify the test to meet requirements, but sometimes doing so will mean losing some of the intent of the test.
Instead, a better approach may be to duplicate the test, and make your modifications, thus preserving the original test as-is.
Any existing e2e test should have gone through a standard review process by a respective SIG in order to have been merged in, which means that the test was most likely reviewed by domain-specific experts. This can be useful to note when modifying tests to better suit conformance concerns, or meet requirements. That said, existings tests are of varying levels of quality. It is important to verify that the test actually does validate the expected behavior, as described in any API documentation, and as specified in the test description you add for promotion.
New tests must go through the standard process for e2e tests even when intended for Conformance from the onset. This means working with SIG-specific reviewers in order to get your PR accepted. After which, the test must be in the test cycle for 2 weeks, to prove its stability. If the test is not slow or flaky, then you may begin the promotion process by following the steps detailed in "Promoting Tests to Conformance".