Add nav testing deps (#506)

Author: simona-anomis

NavigationCodelab/app/build.gradle

@@ -101,6 +101,7 @@ dependencies {
 
     // Testing dependencies
     androidTestImplementation "androidx.arch.core:core-testing:2.2.0"
+    androidTestImplementation "androidx.navigation:navigation-testing:2.8.4"
     androidTestImplementation "androidx.test.espresso:espresso-contrib:3.6.1"
     androidTestImplementation "androidx.test.espresso:espresso-core:3.6.1"