The repository at https://github.com/knative/serving-operator has tests for the upstream Knative Serving operator. These tests can be run against the bits installed by the Serverless operator. There's only one expected failure: TestKnativeServingDeployment/configure (due to https://jira.coreos.com/browse/SRVKS-241).
The goal is to run those tests as part of openshift-knative/serverless-operator repo in CI which would verify the functionality of the Knative Serving Operator which is deployed by the Serverless Operator