How to use the @jupyterlab/docregistry/src.Base64ModelFactory function in @jupyterlab/docregistry

it('should be a no-op a factory with the given `name` is already registered', () => {
        const factory = new Base64ModelFactory();
        registry.addModelFactory(factory);
        const disposable = registry.addModelFactory(new Base64ModelFactory());
        disposable.dispose();
      });

it('should get a registered model factory by name', () => {
        const mFactory = new Base64ModelFactory();
        registry.addModelFactory(mFactory);
        expect(registry.getModelFactory('base64')).to.equal(mFactory);
      });
    });

it('should be a no-op if the same factory is already registered', () => {
        const factory = new Base64ModelFactory();
        registry.addModelFactory(factory);
        const disposable = registry.addModelFactory(factory);
        disposable.dispose();
      });