How to test NGXS in Angular applications

If you need to avoid mocking NGXS in your modules, use .keep.

beforeEach(() =>
   MockBuilder(TargetComponent, TargetModule)
     
     // NgxsModule.forRoot() is called in TargetModule or its imports 
     .keep(NgxsModule.forRoot().ngModule) // keeps all NgxsModule.forRoot
     
     // add it only if your module imports NgxsModule.forFeature
     // NgxsModule.forFeature() is called in TargetModule or its imports
     .keep(NgxsModule.forFeature().ngModule) // keeps all NgxsModule.forFeature
     
     // keeps the root provider of the store
     .keep(Store)
 );

If your module imports only NgxsModule.forFeature, use a test module to initialize NgxsModule.forRoot() before the feature module. Keep Store as a dependency so its NGXS root services stay real:

@NgModule({
  imports: [NgxsModule.forRoot(), TargetModule],
})
class TestModule {}

beforeEach(() =>
   MockBuilder(TargetComponent, TestModule)
     .keep(Store)
     .keep(NgxsModule.forRoot().ngModule)
     .keep(NgxsModule.forFeature().ngModule)
 );