diff --git a/testing-modules/groovy-spock/README.md b/testing-modules/groovy-spock/README.md
index 18d26e8fc0..a98df27172 100644
--- a/testing-modules/groovy-spock/README.md
+++ b/testing-modules/groovy-spock/README.md
@@ -1,3 +1,4 @@
 ### Relevant articles
 
 - [Introduction to Testing with Spock and Groovy](http://www.baeldung.com/groovy-spock)
+- [Difference Between Stub, Mock, and Spy in the Spock Framework](https://www.baeldung.com/spock-stub-mock-spy)