function putObjectMock(bucketName, objectName, fields, cb) {
    const md = fields ? fields.getValue() : baseMd;
    return metadata.putObjectMD(bucketName, objectName, md, {}, log, err => {
        assert.ifError(err);
        return cb();
    });
}
Mocks a Put Object to store custom metadata
@param {string} bucketName - the bucket name
@param {string} objectName - the object name
@param {ObjectMD} fields - custom MD fields to add to the object
@param {Function} cb - callback once the object MD is created
@returns {undefined}