Base primitive to create your own persist adapters. Check /packages/persist-web-storage for product usage or inspiration.

One of the features is that each adapter has storageAtom which you could change for testing purposes.testing package has createMockStorage util. Check out tests of this package

Main types.

export interface PersistRecord {
  data: unknown
  fromState: boolean
  id: number
  timestamp: number
  version: number
  to: number

export interface PersistStorage {
  name: string
  get(ctx: Ctx, key: string): null | PersistRecord
  set(ctx: Ctx, key: string, rec: PersistRecord): void
  clear?(ctx: Ctx, key: string): void
  subscribe?(ctx: Ctx, key: string, callback: Fn<[]>): Unsubscribe

export interface WithPersistOptions<T> {
  /** parse data on init or subscription update @optional */
  fromSnapshot?: Fn<[ctx: Ctx, snapshot: unknown, state?: T], T>
  /** the key! */
  key: string
  /** migration callback which will be called if the version changed  @optional */
  migration?: Fn<[ctx: Ctx, persistRecord: PersistRecord], T>
  /** turn on/off subscription  @default true */
  subscribe?: boolean
  /** time to live in milliseconds @default 10 ** 10 */
  time?: number
  /** transform data before persisting  @optional */
  toSnapshot?: Fn<[ctx: Ctx, state: T], unknown>
  /** version of the data which change used to trigger the migration @default 0 */
  version?: number

export interface WithPersist {
  <T extends Atom>(
      | WithPersistOptions<AtomState<T>>['key']
      | WithPersistOptions<AtomState<T>>,
  ): (anAtom: T) => T