diff --git a/src/app/shared/state/__snapshots__/books.reducer.spec.ts.snap b/src/app/shared/state/__snapshots__/books.reducer.spec.ts.snap
new file mode 100644
index 0000000..6edd607
--- /dev/null
+++ b/src/app/shared/state/__snapshots__/books.reducer.spec.ts.snap
@@ -0,0 +1,49 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Books Reducer should add a newly created book to the state 1`] = `
+Object {
+  "activeBookId": "1",
+  "entities": Object {
+    "1": Object {
+      "earnings": 200000000,
+      "id": "1",
+      "name": "Forrest Gump",
+    },
+  },
+  "ids": Array [
+    "1",
+  ],
+}
+`;
+
+exports[`Books Reducer should load all books when the API loads them all successfully 1`] = `
+Object {
+  "activeBookId": null,
+  "entities": Object {
+    "1": Object {
+      "earnings": 1000000,
+      "id": "1",
+      "name": "Castaway",
+    },
+  },
+  "ids": Array [
+    "1",
+  ],
+}
+`;
+
+exports[`Books Reducer should remove books from the state when they are deleted 1`] = `
+Object {
+  "activeBookId": "1",
+  "entities": Object {
+    "1": Object {
+      "earnings": 1000,
+      "id": "1",
+      "name": "Apollo 13",
+    },
+  },
+  "ids": Array [
+    "1",
+  ],
+}
+`;
diff --git a/src/app/shared/state/books.reducer.spec.ts b/src/app/shared/state/books.reducer.spec.ts
index ace7bc5..9970453 100644
--- a/src/app/shared/state/books.reducer.spec.ts
+++ b/src/app/shared/state/books.reducer.spec.ts
@@ -1,9 +1,61 @@
-// import { BooksApiActions, BooksPageActions } from "src/app/books/actions";
-// import { Book } from "../models/book.model";
-// import { reducer, initialState } from "./book.reducer";
+import { BooksApiActions, BooksPageActions } from "src/app/books/actions";
+import { Book } from "../models/book.model";
+import { reducer, initialState, activeBookId, adapter, selectAll } from "./books.reducer";
 
 describe("Books Reducer", () => {
   it("should return the initial state when initialized", () => {
+    const state = reducer(undefined, { type: "@@init" } as any);
 
+    expect(state).toBe(initialState);
+  });
+
+  it("should load all books when the API loads them all successfully", () => {
+    const books: Book[] = [{ id: "1", name: "Castaway", earnings: 1000000 }];
+    const action = BooksApiActions.booksLoaded({ books });
+
+    const state = reducer(initialState, action);
+
+    expect(state).toMatchSnapshot();
+  });
+
+  it("should add a newly created book to the state", () => {
+    const book: Book = { id: "1", name: "Forrest Gump", earnings: 200000000 };
+    const action = BooksApiActions.bookCreated({ book });
+
+    const state = reducer(initialState, action);
+
+    expect(state).toMatchSnapshot();
+  });
+
+  it("should remove books from the state when they are deleted", () => {
+    const book: Book = { id: "1", name: "Apollo 13", earnings: 1000 };
+    const firstAction = BooksApiActions.bookCreated({ book });
+    const secondAction = BooksPageActions.deleteBook({ book });
+
+    const state = [firstAction, secondAction].reduce(reducer, initialState);
+
+    expect(state).toMatchSnapshot();
+  });
+
+  describe("Selectors", () => {
+    const initialState = { activeBookId: "1", ids: [], entities: {} };
+
+    describe("activeBookId", () => {
+      it("should return the active book id", () => {
+        const result = activeBookId(initialState);
+
+        expect(result).toBe("1");
+      });
+    });
+
+    describe("selectAll", () => {
+      it("should return all the loaded books", () => {
+        const books: Book[] = [{ id: "1", name: "Castaway", earnings: 1000000 }];
+        const state = adapter.addAll(books, initialState);
+        const result = selectAll(state);
+
+        expect(result.length).toBe(1);
+      });
+    });
   });
 });
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