Added short section about jcasc in the testing dev docu (jenkins-infr…

…a#7650)

* added short section about jcasc

* Apply suggestions from code review

Co-authored-by: Kevin Martens <99040580+kmartens27@users.noreply.github.com>

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Co-authored-by: Kevin Martens <99040580+kmartens27@users.noreply.github.com>

content/doc/developer/testing/index.adoc

@@ -568,6 +568,13 @@ public class MyTest {
 }
 ----
 
+=== Verifying compatibility with Configuration as Code (JCasC)
+
+The link:https://plugins.jenkins.io/configuration-as-code/[Configuration as Code plugin] is an opinionated way to configure Jenkins based on human-readable declarative configuration files.
+Writing such a file can be done without being a Jenkins expert by translating a configuration process one is familiar with executing in the web UI into code.
+If the plugin supports JCasC, it also tests compatibility.
+More details can be found in the link:https://github.com/jenkinsci/configuration-as-code-plugin/blob/master/docs/PLUGINS.md[configuration-as-code-plugin documentation].
+
 == Increasing Tests Timeout
 
 The default timeout for Jenkins integration tests is 180 seconds.