diff --git a/src/object-diff.ts b/src/object-diff.ts
index 6c2af89..532a394 100644
--- a/src/object-diff.ts
+++ b/src/object-diff.ts
@@ -5,7 +5,7 @@ import {
   STATUS,
   Subproperties,
 } from "./model";
-import { hasNestedValues, isEqual } from "./utils";
+import { isObject, isEqual } from "./utils";
 
 function getObjectStatus(diff: ObjectDiff["diff"]): DiffStatus {
   return diff.some((property) => property.status !== STATUS.EQUAL)
@@ -26,7 +26,7 @@ function formatSingleObjectDiff(
   }
   const diff: ObjectDiff["diff"] = [];
   Object.entries(data).forEach(([property, value]) => {
-    if (hasNestedValues(value)) {
+    if (isObject(value)) {
       const subPropertiesDiff: Subproperties[] = [];
       Object.entries(value).forEach(([subProperty, subValue]) => {
         subPropertiesDiff.push({
@@ -79,7 +79,7 @@ export function getObjectDiff(
   Object.entries(nextData).forEach(([nextProperty, nextValue]) => {
     const previousValue = prevData[nextProperty];
 
-    if (hasNestedValues(nextValue)) {
+    if (isObject(nextValue)) {
       const prevSubValues = previousValue
         ? Object.entries(previousValue)
         : null;
diff --git a/src/utils.ts b/src/utils.ts
index 098f5f1..55681d5 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1,7 +1,7 @@
 export function isEqual(a: any, b: any): boolean {
-  if (typeof a !== typeof b) return true;
+  if (typeof a !== typeof b) return false;
   if (Array.isArray(a)) {
-    return a.toString() === b.toString();
+    return a.every((v, i) => JSON.stringify(v) === JSON.stringify(b[i]));
   }
   if (typeof a === "object") {
     return JSON.stringify(a) === JSON.stringify(b);
@@ -9,6 +9,6 @@ export function isEqual(a: any, b: any): boolean {
   return a === b;
 }
 
-export function hasNestedValues(value: any): value is Record<string, any> {
-  return typeof value === "object" && !Array.isArray(value);
+export function isObject(value: any): value is Record<string, any> {
+  return !!value && typeof value === "object" && !Array.isArray(value);
 }
diff --git a/test/utils.test.ts b/test/utils.test.ts
index 0096f7f..b751386 100644
--- a/test/utils.test.ts
+++ b/test/utils.test.ts
@@ -1,10 +1,57 @@
-// import { isEqual, hasNestedValues } from "../src/utils";
+import { isEqual, isObject } from "../src/utils";
 
-// describe("isEqual", () => {
-//   it("", () => {
-//     expect(isEqual(null, null)).toStrictEqual(null);
-//   });
-//   it("", () => {
-//     expect(hasNestedValues(null)).toStrictEqual(null);
-//   });
-// });
+describe("isEqual", () => {
+  it("return true if data are the same", () => {
+    expect(isEqual(null, null)).toBeTruthy();
+    expect(isEqual(undefined, undefined)).toBeTruthy();
+    expect(isEqual("hello", "hello")).toBeTruthy();
+    expect(isEqual(57, 57)).toBeTruthy();
+    expect(isEqual(["hello", "world"], ["hello", "world"])).toBeTruthy();
+    expect(
+      isEqual(
+        [
+          { name: "joe", age: 99 },
+          { name: "nina", age: 23 },
+        ],
+        [
+          { name: "joe", age: 99 },
+          { name: "nina", age: 23 },
+        ]
+      )
+    ).toBeTruthy();
+  });
+  it("return false if data are different", () => {
+    expect(isEqual(null, "hello")).toBeFalsy();
+    expect(isEqual("hello", undefined)).toBeFalsy();
+    expect(isEqual("hello", "howdy")).toBeFalsy();
+    expect(isEqual(57, 51)).toBeFalsy();
+    expect(isEqual(["hello", "world"], ["howdy", "world"])).toBeFalsy();
+    expect(
+      isEqual(
+        [
+          { name: "joe", age: 99 },
+          { name: "nina", age: 23 },
+        ],
+        [
+          { name: "joe", age: 98 },
+          { name: "nina", age: 23 },
+        ]
+      )
+    ).toBeFalsy();
+  });
+});
+
+describe("isObject", () => {
+  it("return true if the value has nested values", () => {
+    expect(isObject({ name: "joe" })).toBeTruthy();
+    expect(isObject({ user: { name: "joe" } })).toBeTruthy();
+  });
+  it("return false if the value doesn't have nested values", () => {
+    expect(isObject("joe")).toBeFalsy();
+    expect(isObject(56)).toBeFalsy();
+    expect(isObject(true)).toBeFalsy();
+    expect(isObject(null)).toBeFalsy();
+    expect(isObject(undefined)).toBeFalsy();
+    expect(isObject(["hello", "world"])).toBeFalsy();
+  });
+});