diff --git a/chapter_03-using-stubs-to-break-dependencies/LogAn/fakeExtensionManager.js b/chapter_03-using-stubs-to-break-dependencies/LogAn/fakeExtensionManager.js
new file mode 100644
index 0000000..82c46e0
--- /dev/null
+++ b/chapter_03-using-stubs-to-break-dependencies/LogAn/fakeExtensionManager.js
@@ -0,0 +1,23 @@
+function fakeExtensionManager() {
+    /**
+     * @type {boolean}
+     */
+    let valid = false;
+
+    function willBeValid(value) {
+        valid = value;
+    }
+
+    /**
+     * @param {string} fileName
+     */
+    function isValid(fileName) {
+        return valid;
+    }
+
+    return {
+        willBeValid,
+        isValid,
+    };
+}
+module.exports = fakeExtensionManager;