Add helper message to parser integration test

The parser integration test now has a better message about what to do if
the output changes and how to regenerate it.

Author: DirectXMan12

pkg/crd/parser_integration_test.go

@@ -80,6 +80,6 @@ var _ = Describe("CRD Generation From Parsing to CustomResourceDefinition", func
 		Expect(yaml.Unmarshal(expectedFile, &crd)).To(Succeed())
 
 		By("comparing the two")
-		Expect(parser.CustomResourceDefinitions[groupKind]).To(Equal(crd), "%s", cmp.Diff(parser.CustomResourceDefinitions[groupKind], crd))
+		Expect(parser.CustomResourceDefinitions[groupKind]).To(Equal(crd), "type not as expected, check pkg/crd/testdata/README.md for more details.\n\nDiff:\n\n%s", cmp.Diff(parser.CustomResourceDefinitions[groupKind], crd))
 	})
 })

pkg/crd/testdata/README.md

@@ -0,0 +1,23 @@
+# CRD Integration Test testdata
+
+This contains a tiny module used for testdata for the CRD integration
+test.  The directory should always be called testdata, so Go treats it
+specially.
+
+The `cronjob_types.go` file contains the input types, and is loosely based
+on the CronJob tutorial from the [KubeBuilder
+Book](https://book.kubebuilder.io/cronjob-tutorial.html), but with added
+fields to test additional markers and generation behavior.
+
+If you add a new marker, re-generate the golden output file,
+`testdata.kubebuilder.io_cronjobs.yaml`, with:
+
+```bash
+$ /path/to/current/build/of/controller-gen crd paths=. output:dir=.
+```
+
+Make sure you review the diff to ensure that it only contains the desired
+changes!
+
+If you didn't add a new marker and this output changes, make sure you have
+a good explanation for why generated output needs to change!