Angular-cli: A noob question sorry what is the use of spec.ts?

[hartjo]

i have an issue building my project example in app.component.ts

import { Component } from '@angular/core';

@Component({
  moduleId: module.id,
  selector: 'app-root',
  templateUrl: 'app.component.html',
  styleUrls: ['app.component.css']
})
export class AppComponent {
  title = 'app works!';
}

if i remove the title = 'app works!';

ng build will fail and error output is

ng b -dev

Build failed.
The Broccoli Plugin: [BroccoliTypeScriptCompiler] failed with:
Error: Typescript found the following errors:
  /Users/DarkerThanBlack/Projects/html/ng2-admin/tmp/broccoli_type_script_compiler-input_base_path-y9aTpdto.tmp/0/src/app/app.component.spec.ts (21, 16): Property 'title' does not exist on type 'AppComponent'.
    at BroccoliTypeScriptCompiler._doIncrementalBuild (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/broccoli-typescript.js:120:19)
    at BroccoliTypeScriptCompiler.build (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/broccoli-typescript.js:43:10)
    at /Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/index.js:152:21
    at lib$rsvp$$internal$$tryCatch (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/node_modules/rsvp/dist/rsvp.js:1036:16)
    at lib$rsvp$$internal$$invokeCallback (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/node_modules/rsvp/dist/rsvp.js:1048:17)
    at lib$rsvp$$internal$$publish (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/node_modules/rsvp/dist/rsvp.js:1019:11)
    at lib$rsvp$asap$$flush (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/node_modules/rsvp/dist/rsvp.js:1198:9)
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickCallback (internal/process/next_tick.js:98:9)

The broccoli plugin was instantiated at:
    at BroccoliTypeScriptCompiler.Plugin (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/node_modules/broccoli-plugin/index.js:10:31)
    at BroccoliTypeScriptCompiler.CachingWriter [as constructor] (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/broccoli-caching-writer/index.js:21:10)
    at BroccoliTypeScriptCompiler (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/broccoli-typescript.js:27:5)
    at Angular2App._getTsTree (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/angular2-app.js:321:18)
    at Angular2App._buildTree (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/angular2-app.js:116:23)
    at new Angular2App (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/lib/broccoli/angular2-app.js:53:23)
    at module.exports (/Users/DarkerThanBlack/Projects/html/ng2-admin/angular-cli-build.js:10:10)
    at Class.module.exports.Task.extend.setupBroccoliBuilder (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/lib/models/builder.js:55:19)
    at Class.module.exports.Task.extend.init (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/lib/models/builder.js:89:10)
    at new Class (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/node_modules/core-object/core-object.js:18:12)
    at Class.module.exports.Task.extend.run (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/lib/tasks/build.js:15:19)
    at /Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/lib/commands/build.js:32:24
    at lib$rsvp$$internal$$tryCatch (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/node_modules/rsvp/dist/rsvp.js:1036:16)
    at lib$rsvp$$internal$$invokeCallback (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/node_modules/rsvp/dist/rsvp.js:1048:17)
    at /Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/node_modules/rsvp/dist/rsvp.js:331:11
    at lib$rsvp$asap$$flush (/Users/DarkerThanBlack/Projects/html/ng2-admin/node_modules/angular-cli/node_modules/angular-cli/node_modules/rsvp/dist/rsvp.js:1198:9)

[elvirdolic]

Spec files are generated when you use angular-cli they contain your unit tests for the generated componet or service. In your case you removed sonething from the component and you have todo that alsobin your specs otherwise the project can't build

[val-samonte]

you can just comment out the specific test on the spec file:
// it('should have as title ...
see Test Driven Development to learn more

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