feat: Add note for project dependency gotcha in mockgcp docs

docs/develop-resources/deep-dives/1-add-mockgcp-tests.md

@@ -29,6 +29,12 @@ Create a directory for your resource [pkg/test/resourcefixture/testdata/basic](p
 Just to add the `create.yaml`,  `update.yaml` and `dependencies.yaml` (if applicable) to each bottommost directory.
 These three files are all Kubernetes config files, except that `create.yaml` and `update.yaml` only holds the your Config Connector CR object, and the `dependencies.yaml` holds all the dependent objects.
 
+Note: Do not add your GCP Project as a dependency in `dependencies.yaml` (even with the `cnrm.cloud.google.com/deletion-policy: abandon` annotation). Adding your project as a dependency will cause Config Connector to add the label `cnrm-test: true` to your project during test runs, which likely not desirable. Instead, you can refer to your development project in the `create.yaml` and `update.yaml` resources via an external project reference, with the `${projectId}` template variable. For example:
+```
+  projectRef:
+    external: ${projectId}
+```
+
 ## 1.2 Write the MockGCP server
 
 Follow [this guide](https://github.com/GoogleCloudPlatform/k8s-config-connector/blob/master/mockgcp/README.md) to write a mock gcp server.