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

I'm new to Angular 2 (and Angular in general...) and am finding it very engaging. I am using Angular CLI to generate and serve projects. It seems to work well – though for my little learning projects, it produces more than I need – but that's to be expected.

I've noticed that it generates spec.ts for each Angular element in a project (Component, Service, Pipe, etc). I've searched around but have not found an explanation of what these files are for.

Are these build files which are normally hidden when using tsc? I wondered because I wanted to change the name of a poorly named Component I'd created and discovered that the name was also referenced in these spec.ts files.

import {
  beforeEach,
  beforeEachProviders,
  describe,
  expect,
  it,
  inject,
} from '@angular/core/testing';
import { ComponentFixture, TestComponentBuilder } from '@angular/compiler/testing';
import { Component } from '@angular/core';
import { By } from '@angular/platform-browser';
import { PovLevelComponent } from './pov-level.component';

describe('Component: PovLevel', () => {
  let builder: TestComponentBuilder;

  beforeEachProviders(() => [PovLevelComponent]);
  beforeEach(inject([TestComponentBuilder], function (tcb: TestComponentBuilder) {
    builder = tcb;
  }));

  it('should inject the component', inject([PovLevelComponent],
      (component: PovLevelComponent) => {
    expect(component).toBeTruthy();
  }));

  it('should create the component', inject([], () => {
    return builder.createAsync(PovLevelComponentTestController)
      .then((fixture: ComponentFixture<any>) => {
        let query = fixture.debugElement.query(By.directive(PovLevelComponent));
        expect(query).toBeTruthy();
        expect(query.componentInstance).toBeTruthy();
      });
  }));
});

@Component({
  selector: 'test',
  template: `
    <app-pov-level></app-pov-level>
  `,
  directives: [PovLevelComponent]
})
class PovLevelComponentTestController {
}