Add content for Integration Testing (#1036)

Add a description and resources for Integration Testing

content/roadmaps/101-backend/content/112-testing/100-integration-testing.md

@@ -1 +1,7 @@
-# Integration testing
+# Integration Testing
+
+Integration testing a broad category of tests where multiple software modules are __integrated__ and tested as a group. It is meant to test the __interaction__ between multiple services, resources, or modules. For example, an API's interaction with a backend service, or a service with a database.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.guru99.com/integration-testing.html'>Integration Testing</BadgeLink>
+<BadgeLink badgeText='Watch' href='https://youtu.be/QYCaaNz8emY'>What is Integration Testing?</BadgeLink>