How to use the @loopback/openapi-spec-builder.anOpenApiSpec function in @loopback/openapi-spec-builder

function givenNumberOfRoutes(base: string, num: number) {
  const spec = anOpenApiSpec();
  let i = 0;
  while (i < num) {
    // Add 1/4 paths with vars
    if (i % 4 === 0) {
      spec.withOperationReturningString(
        'get',
        `${base}/group${i}/{version}`,
        `greet${i}`,
      );
    } else {
      spec.withOperationReturningString(
        'get',
        `${base}/group${i}/version_${i}`,
        `greet${i}`,
      );
    }

it('returns spec defined via @api()', () => {
    const expectedSpec = anOpenApiSpec()
      .withOperationReturningString('get', '/greet', 'greet')
      .build();

    @api(expectedSpec)
    class MyController {
      greet() {
        return 'Hello world!';
      }
    }

    const actualSpec = getControllerSpec(MyController);
    expect(actualSpec).to.eql(expectedSpec);
  });

it('preserves routes specified in app.api()', () => {
    function status() {}
    server.api(
      anOpenApiSpec()
        .withOperation('get', '/status', {
          'x-operation': status,
          responses: {},
        })
        .build(),
    );

    function greet() {}
    server.route('get', '/greet', {responses: {}}, greet);

    const spec = server.getApiSpec();
    expect(spec.paths).to.eql({
      '/greet': {
        get: {
          responses: {},
        },

it('finds simple "GET /hello/world" endpoint', () => {
    const spec = anOpenApiSpec()
      .withOperationReturningString('get', '/hello/{msg}', 'greet')
      .withOperationReturningString('get', '/hello/world', 'greetWorld')
      .build();

    class TestController {}

    const table = givenRoutingTable();
    table.registerController(spec, TestController);

    const request = givenRequest({
      method: 'get',
      url: '/hello/world',
    });

    const route = table.find(request);
    expect(route)

async function givenAppWithController() {
    await givenAnApplication();
    app.bind('application.name').to('SequenceApp');

    const apispec = anOpenApiSpec()
      .withOperation('get', '/name', {
        'x-operation-name': 'getName',
        responses: {
          '200': {
            schema: {
              type: 'string',
            },
            description: '',
          },
        },
      })
      .build();

    @api(apispec)
    class InfoController {
      constructor(@inject('application.name') public appName: string) {}

function givenControllerInApp() {
    const apispec = anOpenApiSpec()
      .withOperation('get', '/whoAmI', {
        'x-operation-name': 'whoAmI',
        responses: {
          '200': {
            description: '',
            schema: {
              type: 'string',
            },
          },
        },
      })
      .build();

    @api(apispec)
    class MyController {
      constructor(

function givenControllerInApp() {
    const apispec = anOpenApiSpec()
      .withOperation('get', '/whoAmI', {
        'x-operation-name': 'whoAmI',
        responses: {
          '200': {
            description: '',
            schema: {
              type: 'string',
            },
          },
        },
      })
      .build();

    @api(apispec)
    class MyController {
      constructor(@inject(SecurityBindings.USER) private user: UserProfile) {}

function givenControllerInApp() {
    const apispec = anOpenApiSpec()
      .withOperation('get', '/whoAmI', {
        'x-operation-name': 'whoAmI',
        responses: {
          '200': {
            description: '',
            schema: {
              type: 'string',
            },
          },
        },
      })
      .build();

    @api(apispec)
    class MyController {
      constructor() {}

function givenControllerInApp() {
    const apispec = anOpenApiSpec()
      .withOperation('get', '/whoAmI', {
        'x-operation-name': 'whoAmI',
        responses: {
          '200': {
            description: '',
            schema: {
              type: 'string',
            },
          },
        },
      })
      .build();

    @api(apispec)
    class MyController {
      constructor(