feat(signals): add unprotected testing helper

modules/signals/spec/state-source.spec.ts

@@ -3,17 +3,21 @@ import {
   effect,
   EnvironmentInjector,
   Injectable,
+  signal,
 } from '@angular/core';
 import { TestBed } from '@angular/core/testing';
 import {
   getState,
+  isWritableStateSource,
   patchState,
   signalState,
   signalStore,
+  StateSource,
   watchState,
   withHooks,
   withMethods,
   withState,
+  WritableStateSource,
 } from '../src';
 import { STATE_SOURCE } from '../src/state-source';
 import { createLocalService } from './helpers';
@@ -32,6 +36,24 @@ describe('StateSource', () => {
     [SECRET]: 'secret',
   };
 
+  describe('isWritableStateSource', () => {
+    it('returns true for a writable StateSource', () => {
+      const stateSource: StateSource<typeof initialState> = {
+        [STATE_SOURCE]: signal(initialState),
+      };
+
+      expect(isWritableStateSource(stateSource)).toBe(true);
+    });
+
+    it('returns false for a readonly StateSource', () => {
+      const stateSource: StateSource<typeof initialState> = {
+        [STATE_SOURCE]: signal(initialState).asReadonly(),
+      };
+
+      expect(isWritableStateSource(stateSource)).toBe(false);
+    });
+  });
+
   describe('patchState', () => {
     [
       {

modules/signals/src/index.ts

@@ -12,6 +12,7 @@ export {
 } from './signal-store-models';
 export {
   getState,
+  isWritableStateSource,
   PartialStateUpdater,
   patchState,
   StateSource,

modules/signals/src/state-source.ts

@@ -3,6 +3,7 @@ import {
   DestroyRef,
   inject,
   Injector,
+  isSignal,
   Signal,
   untracked,
   WritableSignal,
@@ -29,6 +30,17 @@ export type StateWatcher<State extends object> = (
   state: NoInfer<State>
 ) => void;
 
+export function isWritableStateSource<State extends object>(
+  stateSource: StateSource<State>
+): stateSource is WritableStateSource<State> {
+  return (
+    'set' in stateSource[STATE_SOURCE] &&
+    'update' in stateSource[STATE_SOURCE] &&
+    typeof stateSource[STATE_SOURCE].set === 'function' &&
+    typeof stateSource[STATE_SOURCE].update === 'function'
+  );
+}
+
 export function patchState<State extends object>(
   stateSource: WritableStateSource<State>,
   ...updaters: Array<

modules/signals/testing/index.ts

@@ -0,0 +1 @@
+export * from './src/index';

modules/signals/testing/ng-package.json

@@ -0,0 +1,5 @@
+{
+  "lib": {
+    "entryFile": "index.ts"
+  }
+}

modules/signals/testing/spec/types/helpers.ts

@@ -0,0 +1,12 @@
+export const compilerOptions = () => ({
+  moduleResolution: 'node',
+  target: 'ES2022',
+  baseUrl: '.',
+  experimentalDecorators: true,
+  strict: true,
+  noImplicitAny: true,
+  paths: {
+    '@ngrx/signals': ['./modules/signals'],
+    '@ngrx/signals/testing': ['./modules/signals/testing'],
+  },
+});

modules/signals/testing/spec/types/uprotected.types.spec.ts

@@ -0,0 +1,53 @@
+import { expecter } from 'ts-snippet';
+import { compilerOptions } from './helpers';
+
+describe('unprotected', () => {
+  const expectSnippet = expecter(
+    (code) => `
+        import { computed, inject } from '@angular/core';
+        import { signalStore, withState, withComputed } from '@ngrx/signals';
+        import { unprotected } from '@ngrx/signals/testing';
+
+        ${code}
+      `,
+    compilerOptions()
+  );
+
+  it('replaces StateSource with WritableStateSource', () => {
+    const snippet = `
+      const CounterStore = signalStore(
+        withState({ count: 0 }),
+        withComputed(({ count }) => ({
+          doubleCount: computed(() => count() * 2),
+        })),
+      );
+
+      const store = inject(CounterStore);
+      const unprotectedStore = unprotected(store);
+    `;
+
+    expectSnippet(snippet).toSucceed();
+    expectSnippet(snippet).toInfer(
+      'unprotectedStore',
+      '{ count: Signal<number>; doubleCount: Signal<number>; [STATE_SOURCE]: WritableSignal<{ count: number; }>; }'
+    );
+  });
+
+  it('does not affect the store with an unprotected state', () => {
+    const snippet = `
+      const CounterStore = signalStore(
+        { protectedState: false },
+        withState({ count: 0 }),
+      );
+
+      const store = inject(CounterStore);
+      const unprotectedStore = unprotected(store);
+    `;
+
+    expectSnippet(snippet).toSucceed();
+    expectSnippet(snippet).toInfer(
+      'unprotectedStore',
+      '{ count: Signal<number>; [STATE_SOURCE]: WritableSignal<{ count: number; }>; }'
+    );
+  });
+});

modules/signals/testing/spec/unprotected.spec.ts

@@ -0,0 +1,29 @@
+import { signal } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+import { patchState, signalStore, StateSource, withState } from '@ngrx/signals';
+import { STATE_SOURCE } from '../../src/state-source';
+import { unprotected } from '../src';
+
+describe('unprotected', () => {
+  it('returns writable state source', () => {
+    const CounterStore = signalStore(
+      { providedIn: 'root' },
+      withState({ count: 0 })
+    );
+
+    const counterStore = TestBed.inject(CounterStore);
+    patchState(unprotected(counterStore), { count: 1 });
+
+    expect(counterStore.count()).toBe(1);
+  });
+
+  it('throws error when provided state source is not writable', () => {
+    const readonlySource: StateSource<{ count: number }> = {
+      [STATE_SOURCE]: signal({ count: 0 }).asReadonly(),
+    };
+
+    expect(() => unprotected(readonlySource)).toThrowError(
+      '@ngrx/signals: The provided source is not writable.'
+    );
+  });
+});

modules/signals/testing/src/index.ts

@@ -0,0 +1 @@
+export { unprotected } from './unprotected';

modules/signals/testing/src/unprotected.ts

@@ -0,0 +1,23 @@
+import {
+  isWritableStateSource,
+  Prettify,
+  StateSource,
+  WritableStateSource,
+} from '@ngrx/signals';
+
+type UnprotectedSource<Source extends StateSource<object>> =
+  Source extends StateSource<infer State>
+    ? Prettify<
+        Omit<Source, keyof StateSource<State>> & WritableStateSource<State>
+      >
+    : never;
+
+export function unprotected<Source extends StateSource<object>>(
+  source: Source
+): UnprotectedSource<Source> {
+  if (isWritableStateSource(source)) {
+    return source as UnprotectedSource<Source>;
+  }
+
+  throw new Error('@ngrx/signals: The provided source is not writable.');
+}

projects/ngrx.io/content/guide/signals/signal-store/testing.md

@@ -19,7 +19,7 @@ A key concern in testing is maintainability. The more tests are coupled to inter
 
 For example, when testing the store in a loading state, avoid directly setting the loading property. Instead, trigger a loading method and assert against an exposed computed property or slice. This approach reduces dependency on internal implementations, such as properties set during the loading state.
 
-From this perspective, private properties or methods of the SignalStore should not be accessed. Additionally, avoid running `patchState` if the state is protected.
+From this perspective, private properties or methods of the SignalStore should not be accessed.
 
 ---
 
@@ -118,6 +118,35 @@ describe('MoviesStore', () => {
 
 </code-example>
 
+### `unprotected`
+
+The `unprotected` function from the `@ngrx/signals/testing` plugin is used to update the protected state of a SignalStore for testing purposes.
+This utility bypasses state encapsulation, making it possible to test state changes and their impacts.
+
+```ts
+// counter.store.ts
+const CounterStore = signalStore(
+  { providedIn: 'root' },
+  withState({ count: 1 }),
+  withComputed(({ count }) => ({
+    doubleCount: computed(() => count() * 2),
+  })),
+);
+
+// counter.store.spec.ts
+import { TestBed } from '@angular/core/testing';
+import { unprotected } from '@ngrx/signals/testing';
+
+describe('CounterStore', () => {
+  it('recomputes doubleCount on count changes', () => {
+    const counterStore = TestBed.inject(CounterStore);
+
+    patchState(unprotected(counterStore), { count: 10 });
+    expect(counterStore.doubleCount()).toBe(20);
+  });
+});
+```
+
 ### `withComputed`
 
 Testing derived values of `withComputed` is also straightforward.

tsconfig.json

@@ -46,6 +46,7 @@
       "@ngrx/signals": ["./modules/signals"],
       "@ngrx/signals/entities": ["./modules/signals/entities"],
       "@ngrx/signals/rxjs-interop": ["./modules/signals/rxjs-interop"],
+      "@ngrx/signals/testing": ["./modules/signals/testing"],
       "@ngrx/signals/schematics-core": ["./modules/signals/schematics-core"],
       "@ngrx/store": ["./modules/store"],
       "@ngrx/store-devtools": ["./modules/store-devtools"],