diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..0886a5278 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,9 +1,3 @@
-// Predict and explain first...
-
-// This code should log out the houseNumber from the address object
-// but it isn't working...
-// Fix anything that isn't working
-
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +6,4 @@ 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..925ea5f54 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,7 +1,6 @@
-// Predict and explain first...
-
-// 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
+// explanation:
+// The code could not be executed because the for...of loop could not access object "author".
+// for...loops are used in arrays, strings or with certain array methods.
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +10,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..e6230ac41 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,9 +1,3 @@
-// Predict and explain first...
-
-// 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?
-
 const recipe = {
   title: "bruschetta",
   serves: 2,
@@ -12,4 +6,4 @@ 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..f96b86673 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,8 @@
-function contains() {}
+function contains(object, property) {
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    throw new Error("contains requires an object");
+  }
+  return Object.hasOwn(object, property);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 719272787..2be0788d7 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -1,19 +1,5 @@
 const contains = require("./contains.js");
 
-/*
-Implement a function called contains that checks an object contains a
-particular property
-
-E.g. contains({a: 1, b: 2}, 'a') // returns true
-as the object contains a key of 'a'
-
-E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
-
-E.g. contains([1, 2, 3], 'a') throws Error("contains requires an object")
-as an array isn't an object
-*/
-
 // Acceptance criteria:
 
 // Given a contains function
@@ -23,18 +9,47 @@ as an array isn't an object
 // 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", () => {
+  expect(contains({}, "name")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains on object with existing property returns true", () => {
+  expect(contains({ name: "Moses", age: 30 }, "name")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains on object with non-existent property returns false", () => {
+  expect(contains({ name: "Moses", age: 30 }, "city")).toBe(false);
+});
 
 // Given a value that isn't an object - an array, a string, a number,
 // null, or no argument at all
 // When passed to contains
 // Then it should throw Error("contains requires an object")
 // (careful: typeof [] and typeof null are both "object")
+test("contains throws an error for an array", () => {
+  expect(() => contains([1, 2, 3], "0")).toThrow("contains requires an object");
+});
+
+test("contains throws an error for a string", () => {
+  expect(() => contains("Manchester", "0")).toThrow(
+    "contains requires an object"
+  );
+});
+
+test("contains throws an error for a number", () => {
+  expect(() => contains(30, "name")).toThrow("contains requires an object");
+});
+
+test("contains throws an error for null", () => {
+  expect(() => contains(null, "name")).toThrow("contains requires an object");
+});
+
+test("contains throws an error when no argument is given", () => {
+  expect(() => contains()).toThrow("contains requires an object");
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..8d214aa97 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,13 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  const lookup = {};
+
+  for (const pair of pairs) {
+    const countryCode = pair[0];
+    const currencyCode = pair[1];
+
+    lookup[countryCode] = currencyCode;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..ada04588c 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,35 +1,11 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
-/*
-
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+test("creates a country currency code lookup for multiple codes", () => {
+  const pairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+  const result = createLookup(pairs);
+
+  expect(result).toEqual({ US: "USD", CA: "CAD" });
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..e457f3e56 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,3 +1,12 @@
+function decode(text) {
+  const withSpaces = text.replace(/\+/g, " ");
+  try {
+    return decodeURIComponent(withSpaces);
+  } catch {
+    return withSpaces;
+  }
+}
+
 function parseQueryString(queryString) {
   const queryParams = {};
   if (queryString.length === 0) {
@@ -6,8 +15,25 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    if (pair === "") continue;
+
+    const index = pair.indexOf("=");
+    const separator = index !== -1;
+    const rawKey = separator ? pair.slice(0, index) : pair;
+    const rawValue = separator ? pair.slice(index + 1) : "";
+
+    const key = decode(rawKey);
+    const value = decode(rawValue);
+
+    if (key in queryParams) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..adbfc2965 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,7 +3,7 @@
 // Below are some test cases the implementation doesn't handle well.
 // Fix the implementation for these tests, 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("should parse values containing '='", () => {
   expect(parseQueryString("equation=a=b-2")).toEqual({
@@ -46,3 +46,8 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+
+// Edge cases
+test("should not crash on malformed percent-encoding", () => {
+  expect(parseQueryString("a=%E0%A4%A")).toEqual({ a: "%E0%A4%A" });
+});
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..e5dbcbcbf 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,18 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally requires an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    if (Object.hasOwn(counts, item)) {
+      counts[item] += 1;
+    } else {
+      counts[item] = 1;
+    }
+  }
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index ca763c296..3ef40e625 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -1,19 +1,5 @@
 const tally = require("./tally.js");
 
-/**
- * tally array
- *
- * In this task, you'll need to implement a function called tally
- * that will take a list of items and count the frequency of each item
- * in an array
- *
- * For example:
- *
- * tally(['a']), target output: { a: 1 }
- * tally(['a', 'a', 'a']), target output: { a: 3 }
- * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
- */
-
 // Acceptance criteria:
 
 // Given a function called tally
@@ -23,12 +9,30 @@ 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 counts duplicate items", () => {
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+});
+test("tally returns count for each unique item", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an invalid input like a string, a number, or no argument at all
 // When passed to tally
 // Then it should throw Error("tally requires an array")
+test("tally throws an error when given an invalid input", () => {
+  expect(() => tally("hello")).toThrow(new Error("tally requires an array"));
+  expect(() => tally(30)).toThrow(new Error("tally requires an array"));
+  expect(() => tally()).toThrow(new Error("tally requires an array"));
+});
+
+// Tally handles items named like built-in object properties
+test("tally handles items named like built-in 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..039621169 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -1,29 +1,30 @@
-// Let's define how invert should work
-
-// Given an object
-// When invert is passed this object
-// Then it should swap the keys and values in the object
-
-// E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
-
 function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
 // a) What is the current return value when invert is called with { a : 1 }
+// Current return value is an object, { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// The current return value is an object also, { key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// The target value is { "1": "a", "2": "b"}
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries returns an array of object [key, value] pairs.
+// It converts an object into an array, so the loop works, since plain objects can't be used with loops.
 
 // d) Explain why the current return value is different from the target output
+// It differs due to the fact that "invertedObj.key" uses the wrong notation, "key", instead of the variable's value.
+// Also, adding brackets to the literal name, [key], would only copy the object not fix it.
 
 // e) 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..1b3933ba8
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,13 @@
+const invert = require("./invert");
+
+test("swaps the key and value of a single pair", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("swaps every pair when there are multiple pairs", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+});
+
+test("returns an empty object when given an empty object", () => {
+  expect(invert({})).toEqual({});
+});