Unit testing strategies

Angular supports unit testing with some of the following:

• Components
• Services
• Pipes

Angular supports the following two different unit testing strategies while performing unit tests with the aforementioned building blocks:

• Isolated unit tests for services and pipes: Isolated unit tests are about testing the block of code in complete isolation, wherein test doubles are used to replace actual dependencies. As test doubles, test instances are created and injected as constructor parameters. One or more APIs are then invoked on these test instances to continue executing the unit tests. It is recommended to use isolated unit tests for services and pipes. 
• Angular testing utilities for components: Testing components in an effective manner, however, would require interacting with the Angular environment due to the need for components to interact with templates, or with other components. This is where the Angular testing utilities come into the picture. The following are some of...