UPSTREAM: <carry>: Update readme Default Catalog Tests

Author: camilamacedo86

openshift/default-catalog-consistency/README.md

@@ -1,19 +1,69 @@
 Default Catalog Consistency
 ========================
 
-Those tests are used to check the consistency of the default catalogs in OpenShift.
+These tests verify the consistency of the default catalogs shipped with OpenShift.
+Default catalogs provide the operator content that OLM manages on every cluster.
+If a catalog is broken, operators cannot be installed or upgraded, which directly
+affects supportability.
 
-### Running Tests
+## What it checks
+
+The test suite reads catalog image references from the ClusterCatalog manifests
+(at `catalogd/manifests.yaml`), pulls each image, and runs four layers of checks:
+
+| Layer | What it validates | Examples |
+|-------|-------------------|----------|
+| **Image** | The container image is well-formed | Valid OCI manifest, has required labels (e.g. `operators.operatorframework.io.index.configs.v1=/configs`) |
+| **Multi-arch** | The image supports all required platforms | linux/amd64, linux/arm64, linux/ppc64le, linux/s390x |
+| **Filesystem** | Expected files and directories exist inside the image | `bin/opm` is a valid Go binary, `configs/` and `tmp/cache/` directories exist |
+| **Catalog (FBC)** | The File-Based Catalog content is valid | No bundles use the deprecated `olm.bundle.object` property; all channel heads have `olm.csv.metadata` |
+
+The check implementations live in `pkg/check/` and the test entry point is
+`test/validate/suite_test.go`.
+
+## CI configuration
+
+CI and periodic jobs are configured in the
+[openshift/release](https://github.com/openshift/release) repository under
+[ci-operator/config/openshift/operator-framework-operator-controller/](https://github.com/openshift/release/tree/master/ci-operator/config/openshift/operator-framework-operator-controller).
+
+### Presubmit
+
+A presubmit job runs on every PR that touches catalog-related files.
+See the [main branch config](https://github.com/openshift/release/blob/master/ci-operator/config/openshift/operator-framework-operator-controller/openshift-operator-framework-operator-controller-main.yaml)
+(search for `default-catalog-consistency`).
+
+### Periodic
+
+Each release branch has a periodic job that runs on a schedule and reports results
+to [Sippy](https://sippy.dptools.openshift.org/sippy-ng/). Look for files ending
+in `__periodics.yaml`, for example:
+
+- [release-4.20 periodics](https://github.com/openshift/release/blob/main/ci-operator/config/openshift/operator-framework-operator-controller/openshift-operator-framework-operator-controller-release-4.20__periodics.yaml)
+
+You can view results per release in Sippy. For example:
+[4.22 default-catalog jobs](https://sippy.dptools.openshift.org/sippy-ng/jobs/4.22?filters=%257B%2522items%2522%253A%255B%257B%2522columnField%2522%253A%2522variants%2522%252C%2522operatorValue%2522%253A%2522has%2520entry%2522%252C%2522value%2522%253A%2522never-stable%2522%252C%2522not%2522%253Atrue%257D%252C%257B%2522id%2522%253A99%252C%2522columnField%2522%253A%2522name%2522%252C%2522operatorValue%2522%253A%2522contains%2522%252C%2522value%2522%253A%2522default-catalog%2522%257D%255D%257D&sort=asc&sortField=net_improvement).
+
+## Monitoring and alerts
+
+When periodic jobs fail, alerts are sent to the `#forum-ocp-catalogs-program` Slack channel.
+[Example alert](https://redhat-internal.slack.com/archives/C08D3G4EMRA/p1777089324894579).
+
+> **Note:** Currently, thresholds are high and many alerts are caused by flakes or
+> infrastructure issues (like the example above). We must still monitor these alerts
+> because a real failure means the default catalogs are broken -- operators cannot be
+> installed or upgraded, and this is critical for the content managed by OLM.
+
+## Running tests locally
 
 ```bash
 make test-catalog
 ```
 
-### Before Pushing Changes
+## Before pushing changes
 
-Before pushing changes to the repository, you should verify that the tests pass. 
-This can be done by running:
+Run the following to verify that tests pass and code is properly formatted:
 
 ```bash
 make verify
-```
+```