How to use the @jupyterlab/rendermime.OutputModel.getMetadata function in @jupyterlab/rendermime

it('should handle output with no metadata field', () => {
        const metadata = OutputModel.getMetadata(DEFAULT_STREAM);
        expect(Object.keys(metadata).length).to.equal(0);
      });
    });

it('should get the metadata from the bundle', () => {
        const metadata = OutputModel.getMetadata(DEFAULT_EXECUTE);
        expect(metadata['foo']).to.equal(1);
        expect(metadata['bar']).to.equal('baz');
      });