add test

packages/toolkit/src/entities/tests/entity_state.test.ts

@@ -35,6 +35,27 @@ describe('Entity State', () => {
     })
   })
 
+  it('should let you provide initial entities', () => {
+    const book1: BookModel = { id: 'a', title: 'First' }
+
+    const initialState = adapter.getInitialState(undefined, [book1])
+
+    expect(initialState).toEqual({
+      ids: [book1.id],
+      entities: { [book1.id]: book1 },
+    })
+
+    const additionalProperties = { isHydrated: true }
+
+    const initialState2 = adapter.getInitialState(additionalProperties, [book1])
+
+    expect(initialState2).toEqual({
+      ...additionalProperties,
+      ids: [book1.id],
+      entities: { [book1.id]: book1 },
+    })
+  })
+
   it('should allow methods to be passed as reducers', () => {
     const upsertBook = createAction<BookModel>('otherBooks/upsert')