Added tests to check for flatten call with null, undefined, symbol keys and circular references

test/unhandledExceptionsTest.js

@@ -0,0 +1,28 @@
+import assert from "node:assert";
+import { describe, test } from "node:test";
+import { flatten, unflatten } from "../index.js";
+
+describe("flatten obj tests", function () {
+  test("Flatten null", function () {
+    assert.deepStrictEqual(flatten(null), null);
+  });
+
+  test("Flatten undefined", function () {
+    assert.deepStrictEqual(flatten(undefined), undefined);
+  });
+
+  test("Flatten object with Symbol keys", function () {
+    const sym = Symbol("test");
+    const obj = { [sym]: "value", regularKey: "regularValue" };
+    const flatObj = flatten(obj);
+
+    assert.strictEqual(flatObj["Symbol(test)"], "value"); // Assuming stringification of symbol keys
+  });
+
+  test("Flatten circular reference", function () {
+    const obj = { name: "John" };
+    obj.self = obj; // Circular reference
+
+    assert.throws(() => flatten(obj), /Circular reference detected/);
+  });
+});