diff --git a/book/testing/Chapter.ipynb b/book/testing/Chapter.ipynb
index 4674171..7c6470a 100644
--- a/book/testing/Chapter.ipynb
+++ b/book/testing/Chapter.ipynb
@@ -358,6 +358,70 @@
     "def test_addition_commutative(a, b):\n",
     "    assert a + b == b + a"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Mocking Dependencies with `pytest-mock`"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Testing is an essential part of Software projects.\n",
+    "\n",
+    "\n",
+    "\n",
+    "Especially unit testing, where you test the smallest piece of code that can be isolated.\n",
+    "\n",
+    "\n",
+    "\n",
+    "They should be independent, and fast & cheap to execute.\n",
+    "\n",
+    "\n",
+    "\n",
+    "But, what if you have some dependencies like API calls or interactions with databases and systems?\n",
+    "\n",
+    "\n",
+    "\n",
+    "Here's where mocking comes into play.\n",
+    "\n",
+    "\n",
+    "\n",
+    "Mocking allows you to replace dependencies and real objects with fake ones which mimic the real behavior.\n",
+    "\n",
+    "\n",
+    "\n",
+    "So, you don't have to rely on the availability of your API, or ask for permission to interact with a database, but you can test your functions isolated and independently.\n",
+    "\n",
+    "\n",
+    "\n",
+    "In Python, you can perform mocking with `pytest-mock`, a wrapper around the built-in mock functionality of Python.\n",
+    "\n",
+    "\n",
+    "\n",
+    "See the example below, where we mock the file removal functionality. We can test it without deleting a file from the disk."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import os\n",
+    "\n",
+    "class UnixFS:\n",
+    "    @staticmethod\n",
+    "    def rm(filename):\n",
+    "        os.remove(filename)\n",
+    "def test_unix_fs(mocker):\n",
+    "    mocker.patch('os.remove')\n",
+    "    UnixFS.rm('file')\n",
+    "    os.remove.assert_called_once_with('file')\n"
+   ]
   }
  ],
  "metadata": {