Refactor tally function to use Object.create(null) for counts; add test for handling prototype keywords correctly

Author: Darkidd77

Sprint-2/implement/tally.js

@@ -3,7 +3,7 @@ function tally(list) {
     throw new Error("Input must be an array");
   }
 
-  const counts = {};
+  const counts = Object.create(null);
 
   for (const item of list) {
     if (counts[item]) {

Sprint-2/implement/tally.test.js

@@ -48,3 +48,14 @@ test("tally counts duplicate items correctly", () => {
 test("tally throws an error for invalid input", () => {
   expect(() => tally("not an array")).toThrow("Input must be an array");
 });
+
+// Given an array with keywords that are also properties of Object.prototype, like "toString"
+// When passed to tally
+// Then it should count them correctly without being affected by the prototype chain
+
+test("tally handles prototype keywords correctly", () => {
+  const input = ["toString", "toString", "valueOf"];
+  const expectedOutput = { toString: 2, valueOf: 1 };
+
+  expect(tally(input)).toEqual(expectedOutput);
+});