diff --git a/docs/api/cozy-client/README.md b/docs/api/cozy-client/README.md
index 538604edb..0017cb807 100644
--- a/docs/api/cozy-client/README.md
+++ b/docs/api/cozy-client/README.md
@@ -201,9 +201,39 @@ Rejects with canceled: true as soon as cancel is called
 
 ***
 
+### createFakeClient
+
+▸ **createFakeClient**(`options?`): [`CozyClient`](classes/CozyClient.md)
+
+Creates a client with pre-filled store
+This can be useful for demo in documentation (e.g. storybook)
+
+*   client.{query,save} are replaced with empty functions
+*   client.stackClient.fetchJSON is replaced with empty functions
+
+*Parameters*
+
+| Name | Type | Description |
+| :------ | :------ | :------ |
+| `options` | `Object` | Options |
+| `options.clientFunctions` | `any` | - |
+| `options.clientOptions` | `any` | - |
+| `options.queries` | `any` | - |
+| `options.remote` | `any` | - |
+
+*Returns*
+
+[`CozyClient`](classes/CozyClient.md)
+
+*Defined in*
+
+[packages/cozy-client/src/mock.js:92](https://github.com/cozy/cozy-client/blob/master/packages/cozy-client/src/mock.js#L92)
+
+***
+
 ### createMockClient
 
-▸ **createMockClient**(`options`): [`CozyClient`](classes/CozyClient.md)
+▸ **createMockClient**(`options?`): [`CozyClient`](classes/CozyClient.md)
 
 Creates a client suitable for use in tests
 
@@ -215,6 +245,7 @@ Creates a client suitable for use in tests
 | Name | Type | Description |
 | :------ | :------ | :------ |
 | `options` | `Object` | Options |
+| `options.clientFunctions` | `any` | - |
 | `options.clientOptions` | `any` | - |
 | `options.queries` | `any` | - |
 | `options.remote` | `any` | - |
@@ -225,7 +256,7 @@ Creates a client suitable for use in tests
 
 *Defined in*
 
-[packages/cozy-client/src/mock.js:45](https://github.com/cozy/cozy-client/blob/master/packages/cozy-client/src/mock.js#L45)
+[packages/cozy-client/src/mock.js:48](https://github.com/cozy/cozy-client/blob/master/packages/cozy-client/src/mock.js#L48)
 
 ***
 
diff --git a/packages/cozy-client/src/mock.js b/packages/cozy-client/src/mock.js
index 55c8f716c..b432c6299 100644
--- a/packages/cozy-client/src/mock.js
+++ b/packages/cozy-client/src/mock.js
@@ -1,3 +1,5 @@
+import merge from 'lodash/merge'
+
 import CozyClient from './CozyClient'
 import { receiveQueryResult, receiveQueryError, initQuery } from './store'
 import { normalizeDoc } from 'cozy-stack-client'
@@ -19,7 +21,7 @@ const fillQueryInsideClient = (client, queryName, queryOptions) => {
   }
 }
 
-const mockedQueryFromMockedRemoteData = remoteData => qdef => {
+const mockedQueryFromMockedRemoteData = remoteData => async qdef => {
   if (!remoteData) {
     return { data: null }
   }
@@ -40,9 +42,59 @@ const mockedQueryFromMockedRemoteData = remoteData => qdef => {
  * @param  {object} [options.queries] Prefill queries inside the store
  * @param  {object} [options.remote] Mock data from the server
  * @param  {object} [options.clientOptions] Options passed to the client
+ * @param  {object} [options.clientFunctions] Functions to overide client functions
+ * @returns {CozyClient}
+ */
+const createMockClient = ({
+  queries,
+  remote,
+  clientOptions,
+  clientFunctions
+} = {}) => {
+  const mockedQuery = jest
+    .fn()
+    .mockImplementation(mockedQueryFromMockedRemoteData(remote))
+
+  const clientFunctionsMerge = merge(
+    {
+      query: mockedQuery,
+      save: jest.fn(),
+      saveAll: jest.fn(),
+      stackClient: {
+        fetchJSON: jest.fn()
+      }
+    },
+    clientFunctions
+  )
+
+  return createFakeClient({
+    queries,
+    remote,
+    clientOptions,
+    clientFunctions: clientFunctionsMerge
+  })
+}
+
+/**
+ * Creates a client with pre-filled store
+ * This can be useful for demo in documentation (e.g. storybook)
+ *
+ * - client.{query,save} are replaced with empty functions
+ * - client.stackClient.fetchJSON is replaced with empty functions
+ *
+ * @param  {object} options Options
+ * @param  {object} [options.queries] Prefill queries inside the store
+ * @param  {object} [options.remote] Mock data from the server
+ * @param  {object} [options.clientOptions] Options passed to the client
+ * @param  {object} [options.clientFunctions] Functions to overide client functions useful for testing
  * @returns {CozyClient}
  */
-const createMockClient = ({ queries, remote, clientOptions }) => {
+const createFakeClient = ({
+  queries,
+  remote,
+  clientOptions,
+  clientFunctions
+} = {}) => {
   const client = new CozyClient(clientOptions || {})
   client.ensureStore()
 
@@ -50,15 +102,11 @@ const createMockClient = ({ queries, remote, clientOptions }) => {
     fillQueryInsideClient(client, queryName, queryOptions)
   }
 
-  client.query = jest
-    .fn()
-    .mockImplementation(mockedQueryFromMockedRemoteData(remote))
+  client.query = mockedQueryFromMockedRemoteData(remote)
 
-  client.save = jest.fn()
-  client.saveAll = jest.fn()
-  client.stackClient.fetchJSON = jest.fn()
+  merge(client, clientFunctions)
 
   return client
 }
 
-export { createMockClient }
+export { createMockClient, createFakeClient }
diff --git a/packages/cozy-client/src/mock.spec.js b/packages/cozy-client/src/mock.spec.js
index 3ed8e01ac..91d0cf4b8 100644
--- a/packages/cozy-client/src/mock.spec.js
+++ b/packages/cozy-client/src/mock.spec.js
@@ -1,15 +1,15 @@
-import { createMockClient } from './mock'
+import { createFakeClient, createMockClient } from './mock'
 
 import { Q } from 'cozy-client'
 
-describe('createMockClient', () => {
+describe('createFakeClient', () => {
   const simpsonsFixture = [
     { _id: 'homer', name: 'Homer' },
     { _id: 'marge', name: 'Marge' }
   ]
 
   it('should mock queries inside the store', () => {
-    const client = createMockClient({
+    const client = createFakeClient({
       queries: {
         simpsons: {
           data: simpsonsFixture,
@@ -34,7 +34,7 @@ describe('createMockClient', () => {
   })
 
   it('should mock query with data passed in "remote" option', async () => {
-    const client = createMockClient({
+    const client = createFakeClient({
       remote: {
         'io.cozy.simpsons': simpsonsFixture
       }
@@ -44,7 +44,7 @@ describe('createMockClient', () => {
   })
 
   it('should mock query even if the doctype has not been mocked', async () => {
-    const client = createMockClient({
+    const client = createFakeClient({
       remote: {
         'io.cozy.simpsons': simpsonsFixture
       }
@@ -52,4 +52,31 @@ describe('createMockClient', () => {
     const simpsons = await client.query(Q('io.cozy.adams'))
     await expect(simpsons.data.map(x => x._id)).toEqual([])
   })
+
+  it('should mock function with clientFunctions', async () => {
+    const client = createFakeClient({
+      clientFunctions: {
+        stackClient: {
+          fetchJSON: () =>
+            Promise.resolve({ data: [{ _id: 'homer', name: 'Homer' }] })
+        }
+      }
+    })
+
+    const simpsons = await client.stackClient.fetchJSON('io.cozy.simpsons')
+    expect(simpsons.data).toEqual([{ _id: 'homer', name: 'Homer' }])
+  })
+
+  describe('createMockClient', () => {
+    it('should mock basic client functions', async () => {
+      const client = createMockClient()
+
+      expect(JSON.stringify(client.query)).toEqual(JSON.stringify(jest.fn()))
+      expect(JSON.stringify(client.save)).toEqual(JSON.stringify(jest.fn()))
+      expect(JSON.stringify(client.saveAll)).toEqual(JSON.stringify(jest.fn()))
+      expect(JSON.stringify(client.stackClient.fetchJSON)).toEqual(
+        JSON.stringify(jest.fn())
+      )
+    })
+  })
 })
diff --git a/packages/cozy-client/types/mock.d.ts b/packages/cozy-client/types/mock.d.ts
index eab68ede8..44ed6dc25 100644
--- a/packages/cozy-client/types/mock.d.ts
+++ b/packages/cozy-client/types/mock.d.ts
@@ -8,11 +8,33 @@
  * @param  {object} [options.queries] Prefill queries inside the store
  * @param  {object} [options.remote] Mock data from the server
  * @param  {object} [options.clientOptions] Options passed to the client
+ * @param  {object} [options.clientFunctions] Functions to overide client functions
  * @returns {CozyClient}
  */
-export function createMockClient({ queries, remote, clientOptions }: {
+export function createMockClient({ queries, remote, clientOptions, clientFunctions }?: {
     queries: object;
     remote: object;
     clientOptions: object;
+    clientFunctions: object;
+}): CozyClient;
+/**
+ * Creates a client with pre-filled store
+ * This can be useful for demo in documentation (e.g. storybook)
+ *
+ * - client.{query,save} are replaced with empty functions
+ * - client.stackClient.fetchJSON is replaced with empty functions
+ *
+ * @param  {object} options Options
+ * @param  {object} [options.queries] Prefill queries inside the store
+ * @param  {object} [options.remote] Mock data from the server
+ * @param  {object} [options.clientOptions] Options passed to the client
+ * @param  {object} [options.clientFunctions] Functions to overide client functions useful for testing
+ * @returns {CozyClient}
+ */
+export function createFakeClient({ queries, remote, clientOptions, clientFunctions }?: {
+    queries: object;
+    remote: object;
+    clientOptions: object;
+    clientFunctions: object;
 }): CozyClient;
 import CozyClient from "./CozyClient";