I have a problem where I want to create an extension for https://external-secrets.io/v0.7.2/ and I want to be able to test it in a CI CD pipeline.

Woulds this allow me to run pulumi (infra as code) to setup a cluster simualtion and run some tests?

The nodes here are fake, they won't actually run your software. For CI/CD clusters I would recommend kind (https://github.com/kubernetes-sigs/kind).