What are the "spec.ts" files generated by Angular CLI for?

.spec.ts file is used for unit testing of your application.

If you don't to get it generated just use --spec=false while creating new Component. Like this

ng generate component --spec=false mycomponentName

The spec files are unit tests for your source files. The convention for Angular applications is to have a .spec.ts file for each .ts file. They are run using the Jasmine javascript test framework through the Karma test runner (https://karma-runner.github.io/) when you use the ng test command.

You can use this for some further reading:

https://angular.io/guide/testing

The .spec.ts files are for unit tests for individual components. You can run Karma task runner through ng test. In order to see code coverage of unit test cases for particular components run ng test --code-coverage

if you generate new angular project using "ng new", you may skip a generating of spec.ts files. For this you should apply --skip-tests option.

ng new ng-app-name --skip-tests