docs(angular): add testing services content (#6914)

src/data/roadmaps/angular/content/testing-services@HU1eTYB321C93qh_U7ioF.md

@@ -1 +1,8 @@
 # Testing Services
+
+To ensure your services function as expected, you can write dedicated tests for them. Services are typically the easiest files to unit test. You can instantiate the service within a `beforeEach` block, invoke its methods, and assert the results.
+
+Visit the following resources to learn more:
+
+- [@official@Angular Official Docs - Testing Services](https://angular.dev/guide/testing/services)
+- [@video@Step by Step implementation of the Calculator Service with Jasmine Specification](https://www.youtube.com/watch?v=yoJDYEq8vSs)