Merge pull request #3289 from Ankitasw/dev-doc-update

docs: Developer guideline to write unit/integration tests in CAPA repo

Author: k8s-ci-robot

docs/book/src/development/conventions.md

@@ -36,3 +36,25 @@ use
 ```
 
 And then within the code you can check the length or range over the slice.
+
+## Tests
+
+There are three types of tests written for CAPA controllers in this repo:
+* Unit tests  
+* Integration tests
+* E2E tests
+
+In these tests, we use [fakeclient](https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/client/fake), [envtest](https://pkg.go.dev/sigs.k8s.io/controller-runtime/pkg/envtest) and [gomock](https://pkg.go.dev/github.com/golang/mock/gomock) libraries based on the requirements of individual test types.
+
+If any new unit, integration or E2E tests has to be added in this repo,we should follow the below conventions.
+
+### Unit tests
+These tests are meant to verify the functions inside the same controller file where we perform sanity checks, functionality checks etc.
+These tests go into the file with suffix *_unit_test.go.
+
+### Integration tests
+These tests are meant to verify the overall flow of the reconcile calls in the controllers to test the flows for all the services/subcomponents of controllers as a whole.
+These tests go into the file with suffix *_test.go.
+
+### E2E tests
+These tests are meant to verify the proper functioning of a CAPA cluster in an environment that resembles a real production environment. For details, refer [here](https://cluster-api-aws.sigs.k8s.io/development/e2e.html).