Update testing in Node.js roadmap (#1652)

* Update testing in Node.js roadmap

* Update content/roadmaps/107-nodejs/content/111-nodejs-testing/readme.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/107-nodejs/content/111-nodejs-testing/readme.md

@@ -1 +1,7 @@
-# Nodejs testing
+# Testing
+
+Software testing is the process of verifying that what we create is doing exactly what we expect it to do. The tests are created to prevent bugs and improve code quality.
+
+The two most common testing approaches are unit testing and end-to-end testing. In the first, we examine small snippets of code, in the second, we test an entire user flow.
+
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.geeksforgeeks.org/difference-between-end-to-end-testing-and-unit-testing/'>Differences between end-to-end testing and unit testing</BadgeLink>