diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..9c79c04d9 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// Answer: when the console.log runs, it will return `My house number is undefined` because `0` is not a key in the object so its value will be undefined
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +13,4 @@ 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..f46621c84 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// Answer: When the code runs, the console.log will output an error in the terminal because you can not use for...of loop for an object, 
+// instead, you use for...in loop
 
 // 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 +13,6 @@ 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..5020d1602 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// Answer: When the code runs, `${recipe}` part of the console.log expression will output the string `[object Object]`
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -12,4 +13,4 @@ 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..6431d8884 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, propertyName) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    throw new TypeError("Invalid input: obj must be a plain object");
+  }
+
+  return obj.hasOwnProperty(propertyName);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..08086d2fa 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -16,20 +16,53 @@ as the object doesn't contains a key of 'c'
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test("Given an input of an object with a property name, returns true if the object contains the property", () => {
+  const objInput = { a: 1 };
+  expect(contains(objInput, "a")).toBe(true);
+  expect(contains(objInput, "t")).toBe(false);
+});
 
 // 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, when passed to contains, returns false", () => {
+  const objInput = {};
+  expect(contains(objInput, "a")).toBe(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, when passed to contains with an existing property name, returns true", () => {
+  const objInput = { name: "Alice", age: 25 };
+  expect(contains(objInput, "age")).toBe(true);
+
+  const edgeCaseInput = { 1: "one", "": "empty" };
+  expect(contains(edgeCaseInput, "")).toBe(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, when passed to contains with a non-existent property name, returns false", () => {
+  const objInput = { name: "Peter", age: 48 };
+  expect(contains(objInput, "gender")).toBe(false);
+
+  const objInput1= { name: "Tayo", age: 10 };
+  expect(contains(objInput1, "location")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("Given invalid parameters, contains throws a TypeError", () => {
+  const invalidInputs = ["hello", null, undefined, 123, true, [], () => {}];
+
+  invalidInputs.forEach(input => {
+    expect(() => contains(input, "a")).toThrow(
+      new TypeError("Invalid input: obj must be a plain object")
+    );
+  });
+});
+
+
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..a8131fd98 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,4 +1,10 @@
-function createLookup() {
+function createLookup(arrayLookUp) {
+  const objLookUp = {};
+
+  for (const [country, currency] of arrayLookUp) {
+    objLookUp[country] = currency;
+  }
+  return objLookUp;
   // implementation here
 }
 
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..a536af982 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,16 @@
 const createLookup = 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 currencyArray = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+  const expectedResult = {
+    US: "USD",
+    CA: "CAD",
+  };
+  expect(createLookup(currencyArray)).toEqual(expectedResult);
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..b496db76c 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,33 @@
 function parseQueryString(queryString) {
+  if (typeof queryString !== "string") {
+    throw new TypeError("Invalid input: Input must be a string");
+  }
   const queryParams = {};
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const index = pair.indexOf("=");
+    let key, value;
+
+    if (index === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, index);
+      value = pair.slice(index + 1);
+    }
+
+    try {
+      key = decodeURIComponent(key);
+      value = decodeURIComponent(value);
+    } catch (err) {
+      throw new Error("Invalid URL-encoded string");
+    }
+
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..5086ac04b 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,10 +3,82 @@
 // 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");
 
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+    equation: "x=y+1",
+  });
+});
+
+test("handles empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("handles empty key", () => {
+  expect(parseQueryString("=value")).toEqual({
+    "": "value",
+  });
+});
+
+test("parses multiple key-value pairs", () => {
+  expect(parseQueryString("a=1&b=2&c=3")).toEqual({
+    a: "1",
+    b: "2",
+    c: "3",
+  });
+});
+
+test("parses values with spaces or special characters", () => {
+  expect(parseQueryString("name=John%20Doe&city=New+York")).toEqual({
+    name: "John Doe",
+    city: "New+York",
+  });
+  expect(parseQueryString("tags%5B%5D=hello%20world")).toEqual({
+    "tags[]": "hello world",
+  });
+});
+
+test("throws TypeError for non-string input", () => {
+  expect(() => parseQueryString(null)).toThrow(TypeError);
+  expect(() => parseQueryString(null)).toThrow(
+    "Invalid input: Input must be a string"
+  );
+
+  expect(() => parseQueryString(undefined)).toThrow(TypeError);
+  expect(() => parseQueryString(undefined)).toThrow(
+    "Invalid input: Input must be a string"
+  );
+
+  expect(() => parseQueryString(123)).toThrow(TypeError);
+  expect(() => parseQueryString(123)).toThrow(
+    "Invalid input: Input must be a string"
+  );
+
+  expect(() => parseQueryString({})).toThrow(TypeError);
+  expect(() => parseQueryString({})).toThrow(
+    "Invalid input: Input must be a string"
+  );
+});
+
+test("handles repeated keys, last value wins", () => {
+  expect(parseQueryString("a=1&a=2")).toEqual({
+    a: "2",
+  });
+});
+
+test("handles trailing '&'", () => {
+  expect(parseQueryString("a=1&b=2&")).toEqual({
+    a: "1",
+    b: "2",
+    "": "", // empty pair after trailing &
+  });
+});
+
+test("handles leading '&'", () => {
+  expect(parseQueryString("&a=1&b=2")).toEqual({
+    "": "", // empty pair before leading &
+    a: "1",
+    b: "2",
   });
 });
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..65263d045 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,19 @@
-function tally() {}
+function tally(arr) {
+  if (!Array.isArray(arr)) {
+    throw new TypeError("Invalid input: Input must be an array");
+  }
+
+  const result = Object.create(null);
+
+  for (const item of arr) {
+    if (result[item]) {
+      result[item] += 1;
+    } else {
+      result[item] = 1;
+    }
+  }
+
+  return result;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..ca94edf40 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/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
+test("tally when passed an array of items, returns an object containing counts for each unique item", () => {
+  expect(tally(["a"])).toEqual({ a: 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("when an array with duplicate items is passed to tally", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("when an invalid input is passed to tally, throws an error", () => {
+  expect(() => tally("house")).toThrow(
+    new TypeError("Invalid input: Input must be an array")
+  );
+});
+
+test("tally handles items that match inherited object properties", () => {
+  expect(tally(["toString", "toString"])).toEqual({ toString: 2 });
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..da315753a 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -8,22 +8,28 @@
 
 function invert(obj) {
   const invertedObj = {};
-
+  if (Object.prototype.toString.call(obj) !== "[object Object]") {
+    throw new TypeError("Invalid input: Input must be a plain object");
+  }
   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 }
+module.exports = invert;
 
+// a) What is the current return value when invert is called with { a : 1 }
+// Answer: { key: 1}
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
-
+// Answer: { key:2}
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
-// c) What does Object.entries return? Why is it needed in this program?
-
-// d) Explain why the current return value is different from the target output
-
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Answer: { '1': 'a', '2': 'b' }
+// d) What does Object.entries return? Why is it needed in this program?
+// Object.entries(obj) returns an array of [key, value] pairs, like: [ [ 'a', 1 ], [ 'b', 2 ] ]
+// e) Explain why the current return value is different from the target output
+// Answer: The current return value is different from the target output because `invertedObj.key`
+// uses the literal string "key" instead of the variable key. To use the variable's value as the property name,
+// we must use bracket notation: invertedObj[value] = key.
+// f) Fix the implementation of invert (and write tests to prove it's fixed!)
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..9ce03a6cd
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,47 @@
+const invert = require("./invert.js");
+
+test("Given an empty object, return an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+test("Given a single key-value pair object, returns a swap value", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+  expect(invert({ 1: 1 })).toEqual({ 1: "1" });
+  expect(invert({ key: true })).toEqual({ true: "key" });
+});
+
+test("Given multiple key-value pairs object, returns a swap value", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+  expect(invert({ 1: "a", 2: "b" })).toEqual({ a: "1", b: "2" });
+  expect(invert({ a: 1, b: "x", c: true })).toEqual({
+    1: "a",
+    x: "b",
+    true: "c",
+  });
+  expect(invert({ a: 1, b: 1 })).toEqual({ 1: "b" });
+  expect(invert({ a: 1, b: 1, c: 1 })).toEqual({ 1: "c" });
+});
+
+test("Given an input that is not a plain object, throws an error", () => {
+  expect(() => invert(null)).toThrowError(
+    new TypeError("Invalid input: Input must be a plain object")
+  );
+  expect(() => invert(undefined)).toThrowError(
+    new TypeError("Invalid input: Input must be a plain object")
+  );
+  expect(() => invert(true)).toThrowError(
+    new TypeError("Invalid input: Input must be a plain object")
+  );
+  expect(() => invert(null)).toThrowError(
+    new TypeError("Invalid input: Input must be a plain object")
+  );
+});
+
+test("handles nested objects and arrays as values", () => {
+  const nestedObj = { a: { x: 1 } };
+  const nestedArray = { b: [1, 2, 3] };
+  // Nested object key becomes "[object Object]"
+  expect(invert(nestedObj)).toEqual({ "[object Object]": "a" });
+  // Array key becomes "1,2,3"
+  expect(invert(nestedArray)).toEqual({ "1,2,3": "b" });
+});
\ No newline at end of file