diff --git a/tests/lib/extension/EntitiesController.spec.ts b/tests/lib/extension/EntitiesController.spec.ts
new file mode 100644
index 0000000..e3f44d0
--- /dev/null
+++ b/tests/lib/extension/EntitiesController.spec.ts
@@ -0,0 +1,261 @@
+import EntitiesController from "$lib/extension/EntitiesController";
+import ChromeStorageArea from "$tests/mocks/ChromeStorageArea";
+import StorageHelper from "$lib/browser/StorageHelper";
+import { TestedEntity, type TestedSettings } from "$tests/stubs/Entity";
+import { randomString } from "$tests/utils";
+import { randomInt } from "crypto";
+
+describe('EntitiesController', () => {
+  let mockedStorage: ChromeStorageArea;
+
+  beforeEach(() => {
+    mockedStorage = new ChromeStorageArea();
+    EntitiesController.storage = new StorageHelper(mockedStorage);
+  });
+
+  it('should throw when storage is not present', async () => {
+    EntitiesController.storage = null;
+
+    const readPromise = EntitiesController.readAllEntities(
+      TestedEntity._entityName,
+      TestedEntity,
+    );
+
+    const deletePromise = EntitiesController.deleteEntity(
+      TestedEntity._entityName,
+      randomString(),
+    );
+
+    const updatePromise = EntitiesController.updateEntity(
+      TestedEntity._entityName,
+      new TestedEntity(randomString(), {
+        numberField: randomInt(1000),
+        stringField: randomString(),
+      }),
+    );
+
+    const subscribe = () => {
+      EntitiesController.subscribeToEntity(TestedEntity._entityName, TestedEntity, vi.fn());
+    }
+
+    await expect(readPromise).rejects.toThrow(Error);
+    await expect(deletePromise).rejects.toThrow(Error);
+    await expect(updatePromise).rejects.toThrow(Error);
+
+    expect(subscribe).toThrow(Error);
+  });
+
+  describe('readAllEntities', () => {
+    it('should return empty array when nothing in the storage yet', async () => {
+      const entities = await EntitiesController.readAllEntities(TestedEntity._entityName, TestedEntity);
+      expect(entities).toHaveLength(0);
+    });
+
+    it('should properly capture different entities from storage', async () => {
+      const storageWithEntities: Record<string, Record<string, Partial<TestedSettings>>> = {
+        [TestedEntity._entityName]: {
+          [randomString()]: {
+            stringField: randomString(),
+            numberField: randomInt(-100_000, 100_000),
+          },
+          [randomString()]: {
+            stringField: randomString(),
+            numberField: randomInt(-100_000, 100_000),
+          },
+        }
+      };
+
+      mockedStorage.insertMockedData(storageWithEntities);
+
+      const loadedEntities = await EntitiesController.readAllEntities(TestedEntity._entityName, TestedEntity);
+
+      expect(loadedEntities).toHaveLength(2);
+
+      for (const entity of loadedEntities) {
+        const rawStorageEntry = storageWithEntities[TestedEntity._entityName][entity.id];
+
+        expect(entity.settings.stringField).toBe(rawStorageEntry.stringField);
+        expect(entity.settings.numberField).toBe(rawStorageEntry.numberField);
+      }
+    });
+  });
+
+  describe('updateEntity', () => {
+    it('should create a storage structure if it is not created yet', async () => {
+      expect(mockedStorage.mockedData).toEqual({});
+
+      const entity = new TestedEntity(randomString(), {
+        stringField: randomString(),
+        numberField: randomInt(100_000),
+      });
+
+      await EntitiesController.updateEntity(TestedEntity._entityName, entity);
+
+      expect(mockedStorage.mockedData).toEqual({
+        [TestedEntity._entityName]: {
+          [entity.id]: {
+            stringField: entity.settings.stringField,
+            numberField: entity.settings.numberField,
+          },
+        },
+      });
+    });
+
+    it('should update entity inside the existing', async () => {
+      const id = randomString();
+      const initialStringValue = randomString();
+      const updatedStringValue = randomString();
+
+      mockedStorage.insertMockedData({
+        [TestedEntity._entityName]: {
+          [id]: {
+            stringField: initialStringValue,
+            numberField: randomInt(100_000),
+          } as TestedSettings,
+        }
+      });
+
+      const [entity] = await EntitiesController.readAllEntities(TestedEntity._entityName, TestedEntity);
+      expect(entity.settings.stringField).toBe(initialStringValue);
+
+      entity.settings.stringField = updatedStringValue;
+      await EntitiesController.updateEntity(TestedEntity._entityName, entity);
+
+      const entityInsideStorage = mockedStorage.mockedData[TestedEntity._entityName][id];
+      expect(entityInsideStorage.stringField).toBe(updatedStringValue);
+    });
+  });
+
+  describe('deleteEntity', () => {
+    it('should initialize the storage structure if delete called', async () => {
+      expect(mockedStorage.mockedData).toEqual({});
+
+      await EntitiesController.deleteEntity(TestedEntity._entityName, randomString());
+
+      expect(mockedStorage.mockedData).toEqual({
+        [TestedEntity._entityName]: {},
+      });
+    });
+
+    it('should delete entity and keep the storage object empty', async () => {
+      const id = randomString();
+      const settings: TestedSettings = {
+        numberField: randomInt(100_000),
+        stringField: randomString(),
+      };
+
+      mockedStorage.insertMockedData({
+        [TestedEntity._entityName]: {
+          [id]: settings,
+        }
+      });
+
+      // Doesn't touch existing instance if ID is not found in the storage
+      await EntitiesController.deleteEntity(TestedEntity._entityName, randomString());
+
+      expect(mockedStorage.mockedData).toEqual({
+        [TestedEntity._entityName]: {
+          [id]: settings,
+        }
+      });
+
+      await EntitiesController.deleteEntity(TestedEntity._entityName, id);
+
+      expect(mockedStorage.mockedData).toEqual({
+        [TestedEntity._entityName]: {}
+      });
+    });
+  });
+
+  describe('subscribeToEntity', () => {
+    it('should notify about changes and return new entities', async () => {
+      let receivedEntities: TestedEntity[] | null = null;
+
+      const subscriber = vi.fn((entities: TestedEntity[]) => {
+        receivedEntities = entities;
+      });
+
+      void EntitiesController.subscribeToEntity(TestedEntity._entityName, TestedEntity, subscriber);
+
+      expect(subscriber).not.toHaveBeenCalled();
+
+      const createdEntity = new TestedEntity(randomString(), {
+        numberField: randomInt(100),
+        stringField: randomString(),
+      });
+
+      await EntitiesController.updateEntity(TestedEntity._entityName, createdEntity);
+
+      await vi.waitFor(() => {
+        expect(subscriber).toHaveBeenCalled();
+      }, {interval: 1, timeout: 10});
+
+      const [firstReceivedEntity] = receivedEntities || [];
+
+      expect(firstReceivedEntity).toBeInstanceOf(TestedEntity);
+      expect(firstReceivedEntity).not.toBe(createdEntity);
+      expect(firstReceivedEntity).toEqual(createdEntity);
+    });
+
+    it('should stop receiving updates once unsubscribed', async () => {
+      const firstSubscriber = vi.fn();
+      const unsubscribeFirst = EntitiesController.subscribeToEntity(TestedEntity._entityName, TestedEntity, firstSubscriber);
+
+      const entity = new TestedEntity(randomString(), {
+        numberField: randomInt(100_000),
+        stringField: randomString(),
+      });
+
+      await EntitiesController.updateEntity(TestedEntity._entityName, entity);
+
+      await vi.waitFor(() => {
+        expect(firstSubscriber).toHaveBeenCalledOnce();
+      }, {interval: 1, timeout: 10});
+
+      firstSubscriber.mockReset();
+      unsubscribeFirst();
+
+      const secondSubscriber = vi.fn();
+      void EntitiesController.subscribeToEntity(TestedEntity._entityName, TestedEntity, secondSubscriber);
+
+      entity.settings.stringField = randomString();
+
+      await EntitiesController.updateEntity(TestedEntity._entityName, entity);
+
+      await vi.waitFor(() => {
+        expect(secondSubscriber).toHaveBeenCalledOnce();
+      }, {interval: 1, timeout: 10});
+
+      expect(firstSubscriber).not.toHaveBeenCalled();
+    });
+
+    it('should not notify when something else was changed in the storage', async () => {
+      const rawStorageSubscriber = vi.fn();
+      const entitiesSubscriber = vi.fn();
+
+      void EntitiesController.storage?.subscribe(rawStorageSubscriber);
+      void EntitiesController.subscribeToEntity(TestedEntity._entityName, TestedEntity, entitiesSubscriber);
+
+      EntitiesController.storage?.write('otherStorage', {
+        someField: randomString(),
+      });
+
+      await EntitiesController.updateEntity(
+        TestedEntity._entityName,
+        new TestedEntity(randomString(), {
+          stringField: randomString(),
+          numberField: randomInt(100_000),
+        }),
+      );
+
+      EntitiesController.storage?.write('otherStorage', {
+        someField: randomString(),
+      });
+
+      await vi.waitFor(() => {
+        expect(entitiesSubscriber).toHaveBeenCalledOnce();
+        expect(rawStorageSubscriber).toHaveBeenCalledTimes(3);
+      }, {timeout: 10, interval: 1});
+    })
+  });
+});