implemented tally function adn wrote test cases for it

Author: fayaz551

Sprint-2/implement/tally.js

@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
 
-module.exports = tally;
+  const result = {};
+
+  for (const item of items) {
+    if (result[item]) {
+      result[item]++;
+    } else {
+      result[item] = 1;
+    }
+  }
+
+  return result;
+}
+
+module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,29 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("tally counts the frequency of each item in an array", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts duplicate items correctly", () => {
+  expect(tally(["x", "y", "x", "z", "y"])).toEqual({ x: 2, y: 2, z: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error for non-array input", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+});