diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..38187ac38 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,7 @@
 // Predict and explain first...
-
+// it will fail because the code is trying to access the houseNumber property of the address object, 
+// but it is not defined correctly. The correct way to access the houseNumber property is to 
+// use dot notation, like this: address.houseNumber.
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that 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..da30f9f5d 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// for...of can’t iterate plain objects directly, so it will throw a TypeError .
 // 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) {
+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..2989288a7 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// The console.log will print the whole object instead of the ingredients list.
 // 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?
@@ -10,6 +10,9 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}`);
+console.log("ingredients:");
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..39cb852ce 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(object, propertyName) {
+	if (object === null || typeof object !== "object" || Array.isArray(object)) {
+		return false;
+	}
+
+	return Object.prototype.hasOwnProperty.call(object, propertyName);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..6f581a9df 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -20,16 +20,27 @@ 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", () => {
+	expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains returns true for an existing property", () => {
+	expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains returns false for a non-existent property", () => {
+	expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("contains returns false for invalid parameters like an array", () => {
+	expect(contains(["a", "b"], "0")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..eed464452 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,20 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  if (!Array.isArray(pairs)) {
+    return {};
+  }
+
+  const lookup = {};
+
+  for (const pair of pairs) {
+    if (!Array.isArray(pair) || pair.length < 2) {
+      continue;
+    }
+
+    const [countryCode, currencyCode] = pair;
+    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..69146cb48 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,22 @@
 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 countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
+
+test("returns an empty object for invalid input", () => {
+  expect(createLookup("not-an-array")).toEqual({});
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..cc43623d3 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,33 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  if (typeof queryString !== "string" || queryString.length === 0) {
+    return queryParams;
+  }
+
+  const normalizedQueryString = queryString.startsWith("?")
+    ? queryString.slice(1)
+    : queryString;
+
+  if (normalizedQueryString.length === 0) {
     return queryParams;
   }
-  const keyValuePairs = queryString.split("&");
+
+  const keyValuePairs = normalizedQueryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (pair.length === 0) {
+      continue;
+    }
+
+    const separatorIndex = pair.indexOf("=");
+    const key = separatorIndex === -1 ? pair : pair.slice(0, separatorIndex);
+    const value = separatorIndex === -1 ? "" : pair.slice(separatorIndex + 1);
+
+    if (key.length === 0) {
+      continue;
+    }
+
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..c01965aa1 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -10,3 +10,23 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("parses a key without = as an empty string value", () => {
+  expect(parseQueryString("debug")).toEqual({
+    debug: "",
+  });
+});
+
+test("ignores empty pairs between separators", () => {
+  expect(parseQueryString("a=1&&b=2&")).toEqual({
+    a: "1",
+    b: "2",
+  });
+});
+
+test("supports query strings starting with ?", () => {
+  expect(parseQueryString("?name=cyf&city=manchester")).toEqual({
+    name: "cyf",
+    city: "manchester",
+  });
+});
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..4db1958e6 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+	if (!Array.isArray(items)) {
+		throw new Error("tally expects an array");
+	}
+
+	const counts = {};
+
+	for (const item of items) {
+		if (counts[item] === undefined) {
+			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 2ceffa8dd..83223ad4e 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -23,12 +23,24 @@ 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 returns counts for each unique item", () => {
+	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("tally throws an error for invalid input", () => {
+	expect(() => tally("not-an-array")).toThrow("tally expects an array");
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..4b667e4ab 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,12 +10,14 @@ 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 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..d2333aa1c
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,18 @@
+const invert = require("./invert.js");
+
+test("inverts a single key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({
+    1: "a",
+  });
+});
+
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({
+    1: "a",
+    2: "b",
+  });
+});
+
+test("returns an empty object for empty input", () => {
+  expect(invert({})).toEqual({});
+});
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..9beafdcc1 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,28 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(text) {
+  if (typeof text !== "string" || text.trim().length === 0) {
+    return {};
+  }
+
+  const normalisedText = text
+    .toLowerCase()
+    .replace(/[.,!?;:]/g, " ");
+
+  const words = normalisedText.split(/\s+/).filter(Boolean);
+  const wordCounts = {};
+
+  for (const word of words) {
+    if (wordCounts[word] === undefined) {
+      wordCounts[word] = 1;
+    } else {
+      wordCounts[word] += 1;
+    }
+  }
+
+  return wordCounts;
+}
+
+module.exports = countWords;
diff --git a/Sprint-2/stretch/count-words.test.js b/Sprint-2/stretch/count-words.test.js
new file mode 100644
index 000000000..2d3b34bca
--- /dev/null
+++ b/Sprint-2/stretch/count-words.test.js
@@ -0,0 +1,19 @@
+const countWords = require("./count-words.js");
+
+test("counts repeated words", () => {
+  expect(countWords("you and me and you")).toEqual({
+    you: 2,
+    and: 2,
+    me: 1,
+  });
+});
+
+test("ignores case and punctuation", () => {
+  expect(countWords("Hello, hello! HELLO?")) .toEqual({
+    hello: 3,
+  });
+});
+
+test("returns empty object for empty input", () => {
+  expect(countWords("")).toEqual({});
+});
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..f341668da 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -8,29 +8,37 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
-  // track frequency of each value
-  let freqs = new Map();
+function getFrequencies(list) {
+  const frequencies = new Map();
 
-  for (let num of list) {
-    if (typeof num !== "number") {
+  for (const item of list) {
+    if (typeof item !== "number") {
       continue;
     }
 
-    freqs.set(num, (freqs.get(num) || 0) + 1);
+    frequencies.set(item, (frequencies.get(item) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
-  let maxFreq = 0;
+  return frequencies;
+}
+
+function getModeFromFrequencies(frequencies) {
+  let maxFrequency = 0;
   let mode;
-  for (let [num, freq] of freqs) {
-    if (freq > maxFreq) {
-      mode = num;
-      maxFreq = freq;
+
+  for (const [value, frequency] of frequencies) {
+    if (frequency > maxFrequency) {
+      mode = value;
+      maxFrequency = frequency;
     }
   }
 
-  return maxFreq === 0 ? NaN : mode;
+  return maxFrequency === 0 ? NaN : mode;
+}
+
+function calculateMode(list) {
+  const frequencies = getFrequencies(list);
+  return getModeFromFrequencies(frequencies);
 }
 
 module.exports = calculateMode;
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..65245f5b1 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -8,20 +8,13 @@ function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    const coinValueInPence = Number.parseInt(coin, 10);
+    total += coinValueInPence * quantity;
   }
 
-  return `£${total / 100}`;
+  return `£${(total / 100).toFixed(2)}`;
 }
 
-const till = {
-  "1p": 10,
-  "5p": 6,
-  "50p": 4,
-  "20p": 10,
-};
-const totalAmount = totalTill(till);
-
 // a) What is the target output when totalTill is called with the till object
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
@@ -29,3 +22,5 @@ const totalAmount = totalTill(till);
 // c) What does coin * quantity evaluate to inside the for...of loop?
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+
+module.exports = totalTill;
diff --git a/Sprint-2/stretch/till.test.js b/Sprint-2/stretch/till.test.js
new file mode 100644
index 000000000..e90cfa7dc
--- /dev/null
+++ b/Sprint-2/stretch/till.test.js
@@ -0,0 +1,16 @@
+const totalTill = require("./till.js");
+
+test("totals till values in pounds", () => {
+  const till = {
+    "1p": 10,
+    "5p": 6,
+    "50p": 4,
+    "20p": 10,
+  };
+
+  expect(totalTill(till)).toBe("£4.40");
+});
+
+test("returns £0.00 for an empty till", () => {
+  expect(totalTill({})).toBe("£0.00");
+});