def validate_kernel_string(self, kernel):
        """ determine if a kernel string is valid, meaning it is in the format
            of {username}/{kernel-slug}.
             Parameters
            ==========
            kernel: the kernel name to validate
        """
        if kernel:
            if '/' not in kernel:
                raise ValueError('Kernel must be specified in the form of '
                                 '\'{username}/{kernel-slug}\'')

            split = kernel.split('/')
            if not split[0] or not split[1]:
                raise ValueError('Kernel must be specified in the form of '
                                 '\'{username}/{kernel-slug}\'')

            if len(split[1]) < 5:
                raise ValueError(
                    'Kernel slug must be at least five characters')