implemented the tally fiunction and added some jest test for the function

Author: Yonatanteklemariam

Sprint-2/implement/lookup.js

@@ -1,8 +1,9 @@
 function createLookup(countrycurrency) {
-  const lookup = {};
+  const lookup = {}; // lookup object is created empty to store the new keys and values mapped from the function
   countrycurrency.map(function ([country, currency]) {
+    // maps every keys and values passed as argument in countrycurrency and stores to the variable names of country and currency
     console.log(`${country}: ${currency}`);
-    lookup[country] = currency;
+    lookup[country] = currency; // this lookup object is then used to store the already mapped keys and values of the countrycurrency
   });
   return lookup;
 }

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,30 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup object for multiple codes", () => {
+  const result = createLookup([
+    ["US", "USD"],
+    ["UAE", "AED"],
+    ["ERI", "ERN"],
+  ]);
+
+  expect(result).toEqual({
+    US: "USD",
+    UAE: "AED",
+    ERI: "ERN",
+  });
+});
+
+test("prints country and currency vertically", () => {
+  console.log = jest.fn(); //mocks the console.log which is used to print out only returned values, but since this test only checks the printed output but not returned values, we do mock the console.log to check the printed output
+
+  createLookup([
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ]);
+
+  expect(console.log).toHaveBeenCalledWith("US: USD");
+  expect(console.log).toHaveBeenCalledWith("CA: CAD");
+});
 
 /*
 

Sprint-2/implement/tally.js

@@ -1,21 +1,14 @@
 function tally(arr) {
-  let counts = {};
+  if (!Array.isArray(arr)) throw new TypeError("Input must be an array");
+  const counts = Object.create(null);
   if (arr.length === 0) {
-    return {};
+    return counts;
   }
-  if (arr !== /^[0-9]A-za-z$/g) {
-    throw new Error("Please Enter Valid Input!");
-  }
-
   for (const item of arr) {
-    if (!/^[A-Za-z0-9]$/.test(item)) {
+    if (typeof item !== "string" || !/^[A-Za-z0-9]+$/.test(item)) {
       throw new Error("Please Enter Valid Input!");
     }
-    if (counts.hasOwnProperty(item)) {
-      counts[item] += 1;
-    } else {
-      counts[item] = 1;
-    }
+    counts[item] = (counts[item] ?? 0) + 1;
   }
   return counts;
 }

Sprint-2/implement/tally.test.js

@@ -19,16 +19,33 @@ 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
+describe("tally", () => {
+  test("Given an array of items, returns counts for each unique item", () => {
+    const input = ["apple", "banana", "apple", "orange", "banana", "apple"];
+    const expected = { apple: 3, banana: 2, orange: 1 };
+    expect(tally(input)).toEqual(expected);
+  });
+  // Given an empty array
+  // When passed to tally
+  // Then it should return an empty object
+  test("tally on an empty array returns an empty object", () => {
+    expect([]).toEqual({});
+  });
 
-// 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");
-
-// Given an array with duplicate items
-// When passed to tally
-// Then it should return counts for each unique item
-
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+  // Given an array with duplicate items
+  // When passed to tally
+  // Then it should return counts for each unique item
+  test("Given an array with duplicate items, returns counts for each unique item", () => {
+    const input = ["x", "x", "y", "x", "y"];
+    const expected = { x: 3, y: 2 };
+    expect(tally(input)).toEqual(expected);
+  });
+  // Given an invalid input like a string
+  // When passed to tally
+  // Then it should throw an error
+  test("Given an array containing an invalid item, throws an Error", () => {
+    expect(() => tally(["valid", "hello world"])).toThrow(
+      "Please Enter Valid Input!"
+    );
+  });
+});