diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..f04f731c8 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// this code should log out undefined because even the object "address" is well defined but the property "houseNumber" is not being correctly accessed in the last line of code.
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +12,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..e9fa5b762 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// it should log out an error because the for statement is not correctly expressed and the prorties of the object are accessed instead of the values.
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
 
@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const value in author) {
+  console.log(author[value]);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..259f9a2ba 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// it should not log out the ingredients property's values because the ingredients are stored in an array and the code is not correctly accessing the array elements.
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
 // How can you fix it?
@@ -12,4 +12,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..a49b5cf01 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,8 @@
-function contains() {}
+function contains(obj, name) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
+  return Object.hasOwn(obj, name);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..9acbfd464 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -20,16 +20,36 @@ as the object doesn't contains a key of 'c'
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("given an empty object, returns false", () => {
+  expect(contains({}, "x")).toEqual(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("given an object with properties, returns true when passed to contains with an existing property name", () => {
+  expect(
+    contains({ gitName: "djebsoft", position: "cyf trainee" }, "gitName")
+  ).toEqual(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("given an object with properties, returns false when passed to contains with a non-existent property name", () => {
+  expect(
+    contains({ gitName: "djebsoft", position: "cyf trainee" }, "age")
+  ).toEqual(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+// "length" is perfect for the test because it's real property on the array itself
+test("given invalid parameters (array), returns false or throws an error", () => {
+  expect(contains(["gitName", "age", "position"], "length")).toBe(false);
+});
+
+test("given invalid parameters (like null or undefined), returns false or throws an error", () => {
+  expect(contains(null, "gitName")).toEqual(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..a5bb64409 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,24 @@
-function createLookup() {
-  // implementation here
+// the first element is the country code
+// the second array is the currency code of the country
+// the function should return an object
+// the keys of the object should be the first element of each inner array (country code)
+// the values of the object should be the second element of each inner array (currency code)
+
+function createLookup(countryCurrencyPairs) {
+  // check if the argument is an array of arrays
+  if (
+    !Array.isArray(countryCurrencyPairs) ||
+    // check if each inner array is an array.
+    countryCurrencyPairs.some((pair) => !Array.isArray(pair)) ||
+    // check if each inner array has two elements.
+    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])
+  ) {
+    throw new Error("Invalid input: expected an array of arrays");
+  }
+  return Object.fromEntries(countryCurrencyPairs);
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..1909a7039 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,18 @@
-const createLookup = require("./lookup.js");
+const Lookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () => {
+  const input = [
+    ["DZ", "DZD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+  const result = {
+    DZ: "DZD",
+    CA: "CAD",
+    GB: "GBP",
+  };
+  expect(Lookup(input)).toEqual(result);
+});
 
 /*
 
@@ -24,7 +36,7 @@ Example
 Given: [['US', 'USD'], ['CA', 'CAD']]
 
 When
-createLookup(countryCurrencyPairs) is called
+Lookup(countryCurrencyPairs) is called
 
 Then
 It should return:
@@ -33,3 +45,37 @@ It should return:
    'CA': 'CAD'
  }
 */
+// Given an invalid input (not 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('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('given arrays with too many elements throw "Invalid input: expected an array of arrays"', () => {
+  const input = [
+    ["US", "USD", "flag"],
+    ["CA", "CAD"],
+  ];
+  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('given arrays with too few elements throw "Invalid input: expected an array of arrays"', () => {
+  const input = [["US", "USD"], ["CA"]];
+  expect(() => Lookup(input)).toThrow(
+    "Invalid input: expected an array of arrays"
+  );
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..cad8592a6 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,20 @@
+// the bug in the code is that it does not handle cases where the query string has two = signs or more between two parameters.
+// in this case we make sure to split the string only at the first = sign.
+// so we use the spread operator.
 function parseQueryString(queryString) {
   const queryParams = {};
+  if (queryString === null || queryString === undefined) {
+    return "invalid query string";
+  }
   if (queryString.length === 0) {
     return queryParams;
   }
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    const [key, ...value] = pair.split("=");
+    // we convert the value array back to a string and we get back the = signs by using it as separator.
+    queryParams[key] = value.join("=");
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..d9171b8c9 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,10 +3,85 @@
 // Below is one test case for an edge case the implementation doesn't handle well.
 // Fix the implementation for this test, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js");
 
+// testing when the query string with a value contains = signs
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+    equation: "x=y+1",
+  });
+});
+
+// testing when the query string has multiple ampersands
+test("parses query string with multiple parameters", () => {
+  expect(parseQueryString("name=Ben&age=45&city=new%20city")).toEqual({
+    name: "Ben",
+    age: "45",
+    city: "new%20city",
+  });
+});
+
+// testing when the query string has two ampersands in a row
+test("parses query string with two ampersands in a row", () => {
+  expect(parseQueryString("name=Ben&&age=45")).toEqual({
+    name: "Ben",
+    "": "",
+    age: "45",
+  });
+});
+
+// testing when the query string has no ampersands
+test("parses query string with no ampersands", () => {
+  expect(parseQueryString("name=Ben")).toEqual({
+    name: "Ben",
+  });
+});
+
+// testing when the query string has no ampersands and no equal signs
+test("parses query string with no ampersands and no equal signs", () => {
+  expect(parseQueryString("name")).toEqual({
+    name: "",
+  });
+});
+
+// testing when the query string is empty
+test("parses query string with empty value", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+// testing when the query string is null
+test("parses query string with null value", () => {
+  expect(parseQueryString(null)).toEqual("invalid query string");
+});
+
+// testing when the query string is undefined
+test("parses query string with undefined value", () => {
+  expect(parseQueryString(undefined)).toEqual("invalid query string");
+});
+
+// testing when a pair ends with equal sign (no value)
+test("parses query string with no equal sign", () => {
+  expect(parseQueryString("name=Ben&age=&city=")).toEqual({
+    name: "Ben",
+    age: "",
+    city: "",
+  });
+});
+
+// testing when a pair starts with equal sign (no key)
+test("parses query string starting with equal sign", () => {
+  expect(parseQueryString("name=Ben&=45")).toEqual({
+    name: "Ben",
+    "": "45",
+  });
+});
+
+// testing when a pair has no equal sign (no value and no key)
+// the pair will be the key and the value will be an empty string
+test("parses query string with no equal sign", () => {
+  expect(parseQueryString("name&age=45&city")).toEqual({
+    name: "",
+    age: "45",
+    city: "",
   });
 });
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..ab2ba96bc 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,13 @@
-function tally() {}
-
+function tally(arr) {
+  if (!Array.isArray(arr)) {
+    throw new Error("invalid input");
+  }
+  // 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;
+  }
+  return result;
+}
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..68e1ec667 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -23,12 +23,60 @@ const tally = require("./tally.js");
 // 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 on an array with duplicates returns correct counts for each unique item", () => {
+  expect(
+    tally([
+      "CYF",
+      "CYF",
+      "AWS",
+      "Capgemini",
+      "Deloitte",
+      "Google",
+      "Slack",
+      "Capgemini",
+    ])
+  ).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(123)).toThrow("invalid input");
+});
+
+// Given an invalid input like an object
+test("given invalid input throws an error", () => {
+  expect(() => tally({})).toThrow("invalid input");
+});
+
+// Given an invalid input like null
+test("given invalid input throws an error", () => {
+  expect(() => tally(null)).toThrow("invalid input");
+});
+
+// Given an invalid input like undefined
+test("given invalid input throws an error", () => {
+  expect(() => tally(undefined)).toThrow("invalid input");
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..e8bd4fb20 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -8,22 +8,32 @@
 
 function invert(obj) {
   const invertedObj = {};
-
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj))
+    return invertedObj;
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+// {key: 1}
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// {key: 2}
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// {"1": "a", "2": "b"}
 
 // c) What does Object.entries return? Why is it needed in this program?
+// it returns an array of the pairs properties [key, value] of the object.
+// it is needed in this program to iterate over the key value pairs of the object to swap them in new object.
 
 // d) Explain why the current return value is different from the target output
+// because first it doesn't swap.
+// second, we're using the dot notation to assign the value where we should user the brackets notation as the key is variable and not a string literal.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+module.exports = invert;
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..927bed307
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,36 @@
+const invert = require("./invert.js");
+// writing some tests.
+// Given an simple ordinary object.
+test("invert on a simple object returns the correct inverted object", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+// Given an object with multiple key value pairs.
+test("invert on an object with multiple key value pairs returns the correct inverted object", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+// Given an object with duplicate values.
+test("invert on an object with duplicate values returns the correct inverted object", () => {
+  expect(invert({ a: 1, b: 1 })).toEqual({ 1: "a", 1: "b" });
+});
+// Given an empty object.
+test("invert on an empty object returns an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+// Given an invalid input like a string.
+test("invert on an invalid input like a string returns an empty object", () => {
+  expect(invert("invalid")).toEqual({});
+});
+
+// Given an invalid input like a number.
+test("invert on an invalid input like a number returns an empty object", () => {
+  expect(invert(123)).toEqual({});
+});
+// Given an invalid input like an array.
+test("invert on an invalid input like an array returns an empty object", () => {
+  expect(invert([1, 2, 3])).toEqual({});
+});
+// Given an invalid input like null or undefined.
+test("invert on an invalid input like null or undefined returns an empty object", () => {
+  expect(invert(null)).toEqual({});
+  expect(invert(undefined)).toEqual({});
+});