Testing components
You may have noticed that whenever we used the Angular CLI to scaffold a new Angular application or generate an Angular artifact, it created some test files for us.
Test files in the Angular CLI contain the word spec in their filename. The filename of a test is the same as the Angular artifact it is testing, followed by the suffix .spec.ts. For example, the test file for the main component of an Angular application is app.component.spec.ts and it resides in the same path as the component file.
We should consider an Angular artifact and its corresponding test one thing. When we change the logic of the artifact, we may need to modify the unit test as well. Placing unit test files with their Angular artifacts makes it easier for us to remember and edit them. It also helps us when we need to refactor our code, such as moving artifacts (not forgetting to move the unit test).
When we scaffold a new Angular application, the Angular CLI automatically...
