fixed all errors to pass all tests

Author: djebsoft

Sprint-2/implement/lookup.js

@@ -9,9 +9,9 @@ function Lookup(countryCurrencyPairs) {
   if (
     !Array.isArray(countryCurrencyPairs) ||
     // check if each inner array is an array.
-    !countryCurrencyPairs.every((pair) => Array.isArray(pair)) ||
+    countryCurrencyPairs.some((pair) => !Array.isArray(pair)) ||
     // check if each inner array has two elements.
-    !countryCurrencyPairs.every((pair) => pair.length === 2)
+    countryCurrencyPairs.some((pair) => pair.length !== 2)
     // we can also use index to check the pair is an array as follows:
     // for (let i = 0; i < countryCurrencyPairs.length; i++)
     //  return Array.isArray(countryCurrencyPairs[i])

Sprint-2/implement/lookup.test.js

@@ -46,28 +46,36 @@ It should return:
  }
 */
 // Given an invalid input (not an array of arrays),
-test('return "Invalid input: expected an array of arrays" for string input', () => {
-  const input = "invalid input: expected an array of arrays";
-  expect(Lookup(input)).toEqual("Invalid input: expected an array of arrays");
+test('given string input throw "Invalid input: expected an array of arrays"', () => {
+  let input = "invalid input: expected an array of arrays";
+  expect(() => Lookup(input)).toThrow(
+    "Invalid input: expected an array of arrays"
+  );
 });
 
 // Given an array where its elements are not arrays,
-test('return "Invalid input: expected an array of arrays" for non-array elements', () => {
-  const input = [["US", "USD"], "CA"];
-  expect(Lookup(input)).toEqual("Invalid input: expected an array of arrays");
+test('given array with non-array elements throw "Invalid input: expected an array of arrays"', () => {
+  let input = [["US", "USD"], "CA"];
+  expect(() => Lookup(input)).toThrow(
+    "Invalid input: expected an array of arrays"
+  );
 });
 
 // Given an array where its elements are arrays with more than two elements,
-test('return "Invalid input: expected an array of arrays" for arrays with too many elements', () => {
+test('given arrays with too many elements throw "Invalid input: expected an array of arrays"', () => {
   const input = [
     ["US", "USD", "flag"],
     ["CA", "CAD"],
   ];
-  expect(Lookup(input)).toEqual("Invalid input: expected an array of arrays");
+  expect(() => Lookup(input)).toThrow(
+    "Invalid input: expected an array of arrays"
+  );
 });
 
 // Given an array where its elements are arrays with less than two elements,
-test('return "Invalid input: expected an array of arrays" for arrays with too few elements', () => {
+test('given arrays with too few elements throw "Invalid input: expected an array of arrays"', () => {
   const input = [["US", "USD"], ["CA"]];
-  expect(Lookup(input)).toEqual("Invalid input: expected an array of arrays");
+  expect(() => Lookup(input)).toThrow(
+    "Invalid input: expected an array of arrays"
+  );
 });

Sprint-2/implement/tally.js

@@ -2,7 +2,8 @@ function tally(arr) {
   if (!Array.isArray(arr)) {
     throw new Error("invalid input");
   }
-  let result = {};
+  // using Object.create(null) to create a plain object without prototype
+  let result = Object.create(null);
   for (let i = 0; i <= arr.length - 1; i++) {
     let item = arr[i];
     result[item] = (result[item] || 0) + 1;

Sprint-2/implement/tally.test.js

@@ -27,13 +27,6 @@ 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 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
@@ -52,18 +45,22 @@ test("tally on an array with duplicates returns correct counts for each unique i
   ).toEqual({ CYF: 2, AWS: 1, Capgemini: 2, Deloitte: 1, Google: 1, Slack: 1 });
 });
 
+test("tally on an array with duplicates returns correct counts for each unique item", () => {
+  expect(tally(["toString", "toString"])).toEqual({ toString: 2 });
+});
+
+// Given an input that you mentioned in the review.
+//test("tally on an array with duplicates returns correct counts for each unique item", () => {
+//  expect(tally(["toString", "toString"])).toEqual({ toString: 2 });
+//});
+
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
 test("given invalid input throws an error", () => {
   expect(() => tally("invalid")).toThrow("invalid input");
 });
 
-// Given an invalid input like a number
-test("given invalid input throws an error", () => {
-  expect(() => tally("invalid")).toThrow("invalid input");
-});
-
 // Given an invalid input like a number
 test("given invalid input throws an error", () => {
   expect(() => tally(123)).toThrow("invalid input");