How to use the virtual-alexa.VirtualAlexa.Builder function in virtual-alexa

beforeEach(() => {
    alexa = VirtualAlexa.Builder()
      .handler("hello-world/hello-world.alexaLambdaHandler") // Lambda function file and name
      .interactionModelFile("hello-world/alexa-model.json")
      .create();
  });

private validateFilesAndBuild(createdEmptyInteractionModelIfNeeded: boolean): VirtualAlexa {
        const builder = VirtualAlexa.Builder().applicationID(this.applicationID).skillURL(this.skillURL);
        let usingInteractionModel = false;

        if (this.locale) {
            builder.locale(this.locale);
            if (!this.interactionModelProvided) {
                // If we don't have an interaction Model and have a locale, search in the default models/.json location
                this.interactionModel = this.interactionModel.replace("en-US", this.locale);
            }
        }

        if (!(this.interactionModelProvided || this.intentSchemaProvided)) {
            // No model provided, we check if default files exists
            if (fs.existsSync(this.interactionModel)) {
                usingInteractionModel = true;
            } else if (!(fs.existsSync(this.intentSchemaFile) && fs.existsSync(this.sampleUtterancesFile)) && !createdEmptyInteractionModelIfNeeded) {
                // Model don't exist in default locations