diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..be549d504 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// prediction before running code: This leads to an error as this isn't an array where values accessed via index/position. values should be accessed via keys/properties in objects.
+//observations after running code: logged out "undefined" for ${address[0]}` as this expression can't be matched with any property inside the object
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +14,4 @@ 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..346552b0d 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// prediction before running code: because accessing values of objects should've been done via dot notation or the square brackets method. 
+//observations after running code: the "for.. of" method only works on iterable objects excluding "plain objects". "For...in" method could be used instead.
 
 // 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 +13,7 @@ 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..0638e9010 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// prediction before running code: this template literal expression: "${recipe}" won't give the expected results for the "ingredients" part.
+// observations after running code: ${recipe}` evaluates to [object Object]. This is because template literal ALONE converts an object into a string with unreadable properties.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -10,6 +12,4 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves} ingredients:\n${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..2a710bf5c 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,11 @@
-function contains() {}
+function contains(object, property) {
+    if (typeof object !== "object" || object == null || Array.isArray(object)) {
+        return false;
+    }
+
+        return object.hasOwnProperty(property); 
+    }
+    
+
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..1bc1eda87 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -20,16 +20,62 @@ 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("contains on empty object returns false", () => {
+    
+    const currentOutput = contains({}, "2");
+    const targetOutput = false;
+    expect(currentOutput).toEqual(targetOutput);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+const user = {
+  id: 101,
+  name: "Amina Yusuf",
+  email: "amina@example.com",
+  isVerified: true,
+};
+test("an object contains an existing property name returns true", () => {
+    const currentOutput = contains(user, "name");
+    const targetOutput = true;
+    expect(currentOutput).toEqual(targetOutput);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
 
+const book = {
+  title: "Harry Potter and the Sorcerer's Stone",
+  author: "J.K. Rowling",
+  publishedYear: 1997,
+  genres: "Fantasy",
+  pages: 309
+};
+
+test("an object doesn't contain a property name returns false", () => {
+    const currentOutput = contains(book, "series");
+    const targetOutput = false;
+    expect(currentOutput).toEqual(targetOutput);
+});
+
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+
+const programmingLanguages = ["JavaScript", "Python", "Java", "C++", "Go", "Rust", "Ruby"];
+const languages = null;
+const name = "Hassan";
+
+test("Returns false when invalid parameters are passed", () => {
+    const currentOutput = contains(programmingLanguages, "3");
+    const targetOutput = false;
+    expect(currentOutput).toEqual(targetOutput);
+    const currentOutput1 = contains(languages, "null");
+    const targetOutput1 = false;
+    expect(currentOutput1).toEqual(targetOutput1);
+    const currentOutput2 = contains(name, "Hassan");
+    const targetOutput2 = false;
+    expect(currentOutput2).toEqual(targetOutput2);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..d24b0eff0 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,6 @@
-function createLookup() {
-  // implementation here
+function createLookup(array) {
+ return Object.fromEntries(array);
+  
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..28e4bab3d 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,19 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+const countryCurrencyPairs = [["US", "USD"], ["GB", "GBP"], ["JP", "JPY"], ["NG", "NGN"], ["IN", "INR"], ["CA", "CAD"]];
+
+test("creates a country currency code lookup for multiple codes", () => {
+  const currentOutput = createLookup(countryCurrencyPairs);
+  const targetOutput = {
+  US: "USD",
+  GB: "GBP",
+  JP: "JPY",
+  NG: "NGN",
+  IN: "INR",
+  CA: "CAD"
+};
+expect(currentOutput).toEqual(targetOutput);
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..3d8d2754b 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -3,14 +3,24 @@ function parseQueryString(queryString) {
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
-  }
+    const separatorIndex = pair.indexOf("=");
 
+     if (separatorIndex === -1) {
+          queryParams[pair] = "";
+       } else {
+          const key = decodeURIComponent(pair.slice(0, separatorIndex));
+          const value = decodeURIComponent(pair.slice(separatorIndex + 1));
+          queryParams[key] = value;
+       }
+   }
   return queryParams;
 }
 
 module.exports = parseQueryString;
+
+
+console.log(parseQueryString("equation=x=y+1"));
\ No newline at end of file
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..ed26cf03a 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -5,8 +5,53 @@
 
 const parseQueryString = require("./querystring.js")
 
+test("parses querystring values containing multiple '=' signs", () => {
+  expect(parseQueryString("name=JohnDoe&age=30&country=Canada&sort=recent&showDetails=true")).toEqual({
+  name: "JohnDoe",
+  age: "30",
+  country: "Canada",
+  sort: "recent",
+  showDetails: "true"
+});
+});
+
+
+
+test("parses an empty querystring & returns an empty object", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+
+
+
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+    equation: "x=y+1",
   });
 });
+
+
+
+
+test("parses querystring values without '=' & returns keys only", () => {
+  expect(parseQueryString("fullName")).toEqual({fullName: "" });
+});
+
+
+
+
+test("parses querystring with duplicate/repeated keys & returns the last key-value pair", () => {
+  expect(parseQueryString("haircut=buzzCut&haircut=mullet&haircut=lowFade&shaver=braun&shaver=philips&shaver=wahl")).toEqual({
+    haircut: "lowFade",
+    shaver: "wahl",
+  });
+});
+
+
+test("parses an encoded querystring & returns decoded key-value pairs", () => {
+  expect(parseQueryString("name=John%20Doe&email=john.doe%40example.com&message=Hello%2C%20how%20are%20you%3F")).toEqual({   
+  name: "John Doe",
+  email: "john.doe@example.com",
+  message: "Hello, how are you?"
+  })
+})
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..ac72490c9 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,11 @@
-function tally() {}
+function tally(list) {
+    if (!Array.isArray(list)) {
+        throw new Error("Invalid input!");
+    }
+    return list.reduce((rep, element) => {
+        rep[element] = (rep[element] || 0) + 1;
+        return rep;
+    }, {});
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..2f2fb90e9 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -23,12 +23,36 @@ 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");
+
+const emptyArray = [];
+
+test("tally on an empty array returns an empty object", () => {
+    const currentOutput = tally(emptyArray);
+    const targetOutput = {};
+    expect(currentOutput).toEqual(targetOutput);
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
 
+const animals = ['cat', 'dog', 'cat', 'bird', 'dog', 'dog', 'rabbit', 'cat'];
+
+test("tally on an array returns an object with the frequency of each item as properties", () => {
+    const currentOutput = tally(animals);
+    const targetOutput = {cat: 3, dog: 3, bird: 1, rabbit: 1};
+    expect(currentOutput).toEqual(targetOutput);
+});
+
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+
+test("tally throws an error when given invalid input", () => {
+    const name = "Hassan";
+    const age = null;
+    const subjectsHobbies = {Math: "puzzles", Science: "experiments", Art: "drawing"};
+    expect(() => tally(name)).toThrow("Invalid input!");
+    expect(() => tally(age)).toThrow("Invalid input!");
+    expect(() => tally(subjectsHobbies)).toThrow("Invalid input!");
+});
\ No newline at end of file
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..6e5f71e0f 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -17,13 +17,55 @@ function invert(obj) {
 }
 
 // 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 }
+// b) What is the current return value when invert is called with 
+//{ 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 key-value pairs from an object. 
+//it's needed in order to loop through each key-value pairs of an object.
 
 // d) Explain why the current return value is different from the target output
+// because line 13 is not written accordingly. The current arrangement always starts with keys and then values.
+// Most importantly, there's a bug. Currently, it returns "key" as if it's a key/property name. Refer to (a & b)
+
+
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+
+const sports = {
+  soccer: "ball",
+  tennis: "racket",
+  basketball: "hoopBall",
+  baseball: "bat",
+  swimming: "goggles",
+};
+
+console.log(invert(sports));
+
+// test("when 'invert' passed an object it returns the object with keys & values swapped.", () => {
+//     expect(invert(sports)).toEqual({
+//       ball: "soccer",
+//       racket: "tennis",
+//       hoopBall: "basketball",
+//       bat: "baseball",
+//       goggles: "swimming",
+//     });
+//   });
+
+