Add instructions on how to add declarative test cases.

Signed-off-by: Humair Khan <[email protected]>

Author: HumairAK

controllers/testdata/README.md

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+# Adding declarative tests
+
+Declarative tests are for simple tests to check for OCP resource creations by DSPO when a `DataSciencePipelinesApplication` (`DSPA`) is created. New test cases can be added by simply adding the deployment resources and their expected manifest pairs within the corresponding `case` folder. 
+
+# Adding a new case example
+
+All declarative test cases can be found in `controllers/testdata/declarative`.
+
+Let's say we want a new test case `case_4` that tests that this `DSPA`...
+
+<details> 
+
+<summary> dspa.yaml</summary>
+
+```yaml
+# dspa.yaml
+apiVersion: datasciencepipelinesapplications.opendatahub.io/v1alpha1
+kind: DataSciencePipelinesApplication
+metadata:
+  name: testdsp4 #ma
+spec:
+  objectStorage:
+    minio:
+      image: minio:test4
+  mlpipelineUI:
+    image: frontend:test4
+```
+</details>
+
+...will deploy this configmap: 
+
+<details> 
+
+<summary> configmap.yaml</summary>
+
+```yaml
+apiVersion: v1
+data:
+  artifact_script: |-
+    #!/usr/bin/env sh
+    push_artifact() {
+        if [ -f "$2" ]; then
+            tar -cvzf $1.tgz $2
+            aws s3 --endpoint ${ARTIFACT_ENDPOINT} cp $1.tgz s3://$ARTIFACT_BUCKET/artifacts/$PIPELINERUN/$PIPELINETASK/$1.tgz
+        else
+            echo "$2 file does not exist. Skip artifact tracking for $1"
+        fi
+    }
+    push_log() {
+        cat /var/log/containers/$PODNAME*$NAMESPACE*step-main*.log > step-main.log
+        push_artifact main-log step-main.log
+    }
+    strip_eof() {
+        if [ -f "$2" ]; then
+            awk 'NF' $2 | head -c -1 > $1_temp_save && cp $1_temp_save $2
+        fi
+    }
+kind: ConfigMap
+metadata:
+  name: ds-pipeline-artifact-script-testdsp4
+  namespace: default
+  labels:
+    app: ds-pipeline-testdsp4
+    component: data-science-pipelines
+
+```
+
+</details>
+
+
+We can do this by first creating a folder `controllers/testdata/declarative/case_4`
+Then adding the DSPA cr in: `controllers/testdata/declarative/case_4/deploy/dspa.yaml` (we want to the test case to `deploy` this DSPA)
+Then adding the configmap resource in: `controllers/testdata/declarative/case_4/expected/created/configmap.yaml`
+Each case requires a configmap, we can add one like this: 
+
+```yaml
+Images:
+  ApiServer: api-server:test4
+  Artifact: artifact-manager:test4
+  PersistentAgent: persistenceagent:test4
+  ScheduledWorkflow: scheduledworkflow:test4
+  ViewerCRD: viewercontroller:test4
+  Cache: ubi-minimal:test4
+  MoveResultsImage: busybox:test4
+  MlPipelineUI: frontend:test4
+  MariaDB: mariadb:test4
+  Minio: minio:test4
+```
+In `controllers/testdata/declarative/case_4/config.yaml`
+
+Then run the tests by running: 
+
+`make test`
+
+You can add more expected resources by adding files in the `../expected/created` folder. To test resources that you do 
+not expect to be created, add them in the `../expected/not_created` folders. Please see `/controllers/testutil/equalities.go` for
+all supported resources.
+
+For more complex tests, it is advised to create tests via logic.