Sorry, this may sound a bit vague, but is there any way for the following make the following scenario happen?
BuildKite builds a project Argo CD deploys BuildKite runs the test against the latest deployment.
Is there a way for BuildKite to kick off the tests once it finds out that Argo CD has deployed the project?
I don't have much Argo CD experience directly, but after doing some digging it sounds like you'll need to add an Argo CD PostSync hook to your resource: https://argoproj.github.io/argo-cd/user-guide/resource_hooks/
And from within the PostSync hook, you can start a new Buildkite build using: https://buildkite.com/docs/apis/rest-api/builds#create-a-build
Hope that helps!