From 3453c9e841a406f80e48d9be81e5b33e2f257dfd Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 8 Jul 2026 10:11:39 +0100
Subject: [PATCH 01/18] Fix error in debug/address.js

---
 Sprint-2/debug/address.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..16001dcd9 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// [MM] - The original code returns undefined because it is trying to call houseNumber by index, rather than by key.
 
 // 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}`);

From 4399fc1bca324323b51b39db0002017c9fc4f139 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 8 Jul 2026 10:28:39 +0100
Subject: [PATCH 02/18] Fix bug in debug/author.js

---
 Sprint-2/debug/author.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..eba40efd3 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// [MM] - The original code does not work because it is trying to loop through an array, rather than an object
 
 // 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 +12,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

From 4a01f99bd53b847337a46382d688b528f65a5742 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 9 Jul 2026 02:16:20 +0100
Subject: [PATCH 03/18] Fix error in debug/recipe.js

---
 Sprint-2/debug/recipe.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..f5ba35eb0 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// [MM] - I expect this programme to log out recipe object rather than the ingredients
 
 // 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 +11,5 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves} ingredients:
+${recipe.ingredients.join("\n")}`);

From 3a207285afc384baf4c79a7ee6742d6b0209a3e7 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 9 Jul 2026 14:29:58 +0100
Subject: [PATCH 04/18] write tests for implement/contains.test.js

---
 Sprint-2/implement/contains.test.js | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..983ec1639 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -16,20 +16,33 @@ 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 object and a property name, returns true if object contains the property, otherwise return false", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  expect(contains({ a: 1, b: 2 }, "c")).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 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("given an object and a property name, returns true if object contains the 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("given an object and a property name, returns false if object does not contain the 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("given an invalid array parameter, returns false", () => {
+  expect(contains([1, 2, 3], 3)).toBe(false);
+});

From 3ce1f746a9c995d4df804988f98989f4d253f144 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 9 Jul 2026 14:54:24 +0100
Subject: [PATCH 05/18] complete function in implement/contains.js

---
 Sprint-2/implement/contains.js | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..3a615dd64 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,16 @@
-function contains() {}
+function contains(object, value) {
+  const isNotObject =
+    typeof object !== "object" ||
+    object === null ||
+    Array.isArray(object) ||
+    Object.keys(object).length < 1;
+
+  if (isNotObject) return false;
+
+  return Object.keys(object).includes(value);
+}
+
+console.log(contains({ a: 1, b: 2 }, "a"));
+console.log(contains(["a", "b"], "a"));
 
 module.exports = contains;

From e0455d0d6e910f7dcf97e50ea24f2924e8e826f6 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Fri, 10 Jul 2026 08:40:13 +0100
Subject: [PATCH 06/18] Refactor implement/contains.js

---
 Sprint-2/implement/contains.js | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index 3a615dd64..d7060e92e 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,13 +1,10 @@
 function contains(object, value) {
   const isNotObject =
-    typeof object !== "object" ||
-    object === null ||
-    Array.isArray(object) ||
-    Object.keys(object).length < 1;
+    typeof object !== "object" || object === null || Array.isArray(object);
 
   if (isNotObject) return false;
 
-  return Object.keys(object).includes(value);
+  return Object.hasOwn(object, value);
 }
 
 console.log(contains({ a: 1, b: 2 }, "a"));

From b603cf44be84976427fb11b59c5ff9e4b54f6a74 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Fri, 10 Jul 2026 09:25:33 +0100
Subject: [PATCH 07/18] Write first test for implement/lookup.test.js

---
 Sprint-2/implement/lookup.test.js | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..7bd50b4a6 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,7 +1,5 @@
 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
@@ -33,3 +31,14 @@ It should return:
    'CA': 'CAD'
  }
 */
+test("maps country codes to currency codes", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});

From 975a820c9c5970ba0e7002101c0754f069528190 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Tue, 14 Jul 2026 15:08:41 +0100
Subject: [PATCH 08/18] Write tests for lookup.test.js

---
 Sprint-2/implement/lookup.test.js | 57 ++++++++++++++++++++++++++-----
 1 file changed, 48 insertions(+), 9 deletions(-)

diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 7bd50b4a6..a70de530b 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -31,14 +31,53 @@ It should return:
    'CA': 'CAD'
  }
 */
-test("maps country codes to currency codes", () => {
-  expect(
-    createLookup([
-      ["US", "USD"],
-      ["CA", "CAD"],
-    ])
-  ).toEqual({
-    US: "USD",
-    CA: "CAD",
+
+describe("createLookup", () => {
+  test("maps country codes to currency codes", () => {
+    expect(
+      createLookup([
+        ["US", "USD"],
+        ["CA", "CAD"],
+      ])
+    ).toEqual({
+      US: "USD",
+      CA: "CAD",
+    });
+  });
+
+  test.each([
+    [
+      "throws when input array is empty",
+      [],
+      "Input must not be an empty array",
+    ],
+    ["throws when input is not an array", "hello", "Input must be an array"],
+    [
+      "throws when input pairs are invalid",
+      [1, 2, 3],
+      "Input must be valid text pairs",
+    ],
+    [
+      "throws when duplicate pairs are provided",
+      [
+        ["US", "USD"],
+        ["US", "USD"],
+      ],
+      "Input must not be duplicated",
+    ],
+  ])("%s", (_title, data, expecteMessage) => {
+    expect(() => createLookup(data).toThrow(expecteMessage));
+  });
+
+  test("throws when country code format is incorrect", () => {
+    expect(() => createLookup([["us", "USD"]])).toThrow(
+      "Country code must be 2 uppercase letters"
+    );
+  });
+
+  test("throws when currency code format is incorrect", () => {
+    expect(() => createLookup([["US", "usd"]])).toThrow(
+      "Currency code must be 3 uppercase letters"
+    );
   });
 });

From e7733131ec9af19f2bd0437cd0f60c82c8cc8f47 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Tue, 14 Jul 2026 15:10:13 +0100
Subject: [PATCH 09/18] Complete lookup.js - all tests pass

---
 Sprint-2/implement/lookup.js | 83 +++++++++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 2 deletions(-)

diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..1c2ef44a0 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,84 @@
-function createLookup() {
-  // implementation here
+function createLookup(data) {
+  validateData(data);
+  return data.reduce((lookup, [country, currency]) => {
+    lookup[country] = currency;
+    return lookup;
+  }, {});
 }
 
+// check for valid pairs
+const isValidPair = (value) =>
+  Array.isArray(value) &&
+  value.length === 2 &&
+  typeof value[0] === "string" &&
+  typeof value[1] === "string";
+
+// check for duplicates
+const normaliseDataPair = ([country, currency]) => `${country}|${currency}`;
+const isDuplicated = (data) =>
+  new Set(data.map(normaliseDataPair)).size !== data.length;
+
+const validateData = (data) => {
+  // check that it is an array
+  if (!Array.isArray(data)) {
+    throw new Error("Input must be an array");
+  }
+  // check that input is not empty
+  if (data.length === 0) {
+    throw new Error("Input must not be empty");
+  }
+
+  // check that the values are valid
+  if (data.some((value) => !isValidPair(value))) {
+    throw new Error("Input must be valid text pairs");
+  }
+
+  // check for duplicates
+  if (isDuplicated(data)) {
+    throw new Error("Input must not be duplicated");
+  }
+
+  // check country code has 2 uppercase letters
+  if (data.some(([country]) => !/^[A-Z]{2}$/.test(country))) {
+    throw new Error("Country code must be 2 uppercase letters");
+  }
+  // check currency code has 3 uppercase letters
+  if (data.some(([, currency]) => !/^[A-Z]{3}$/.test(currency))) {
+    throw new Error("Currency code must be 3 uppercase letters");
+  }
+};
+
+// Handle invalid cases
+const INVALID_CASES = [
+  [[], "Input must not be empty"],
+  ["hello", "Input must be an array"],
+  [[1, 2, 3], "Input must be valid text pairs"],
+  [
+    [
+      ["US", "USD"],
+      ["US", "USD"],
+    ],
+    "Input must not be duplicated",
+  ],
+];
+
+const printInvalidCases = () => {
+  for (const [data, expectedMessage] of INVALID_CASES) {
+    try {
+      createLookup(data);
+      console.log(`Unexpected success for ${JSON.stringify(data)}`);
+    } catch (error) {
+      console.log("-".repeat(50));
+      console.log(
+        `Data: ${JSON.stringify(data)}\nExpected: ${expectedMessage}\nReceived: ${error.message}`
+      );
+    }
+  }
+};
+
+if (require.main === module) {
+  console.log("DATA ERRORS");
+  printInvalidCases();
+  console.log("-".repeat(50));
+}
 module.exports = createLookup;

From dab2b2470603ea96dc014b097e4ed1a1f9921a41 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 15 Jul 2026 18:13:24 +0100
Subject: [PATCH 10/18] Complete implement/querysting.js so that all tests pass

---
 Sprint-2/implement/querystring.js | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..39e232015 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -6,10 +6,22 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
-  }
+    if (pair === "") continue;
+
+    const [keyPart, ...valueParts] = pair.split("=");
+    const rawKey = keyPart.trim("").replace(/\+/g, " ");
+    const rawValue = valueParts.join("=").trim("").replace(/\+/g, " ");
+    const key = decodeURIComponent(rawKey);
+    const value = decodeURIComponent(rawValue);
 
+    if (queryParams[key] === undefined) {
+      queryParams[key] = value;
+    } else if (Array.isArray(queryParams[key])) {
+      queryParams[key].push(value);
+    } else {
+      queryParams[key] = [queryParams[key], value];
+    }
+  }
   return queryParams;
 }
 

From 48482452cbc00a286f521ec48a6cd2fc6d77a304 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 15 Jul 2026 18:19:18 +0100
Subject: [PATCH 11/18] Add edge test cases to querystring.test.js

---
 Sprint-2/implement/querystring.test.js | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..0a5f54ee9 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 +46,17 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+
+test("should return empty object for empty string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("should ignore leading and trailing ampersands", () => {
+  expect(parseQueryString("&a=1&b=2&")).toEqual({ a: "1", b: "2" });
+});
+
+test("should parse keys and values with plus signs and percent encoding", () => {
+  expect(parseQueryString("full+name=John+Doe%21")).toEqual({
+    "full name": "John Doe!",
+  });
+});

From bbb2a56a9a06ba0a4b7dd13a5e8c749a1b1639ba Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 15 Jul 2026 23:51:55 +0100
Subject: [PATCH 12/18] write tests fo tally.test.js

---
 Sprint-2/implement/tally.test.js | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..c1bcac222 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,28 @@ 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("return counts for each unique item", () => {
+  expect(tally(["a", "b", "c"])).toEqual({ a: 1, b: 1, c: 1 });
+  expect(tally([1, 2, 3])).toEqual({ 1: 1, 2: 1, 3: 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("return counts for each unique item of duplicate items", () => {
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws when input is not an array", () => {
+  expect(() => tally("hello")).toThrow("Input must be an array");
+});

From 87eb907dae10c320b5e8b373c9e9aa274269211a Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 15 Jul 2026 23:55:05 +0100
Subject: [PATCH 13/18] complete tally.js - all tests pass

---
 Sprint-2/implement/tally.js | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..b537cdb1f 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,35 @@
-function tally() {}
+function tally(array) {
+  if (!Array.isArray(array)) {
+    throw new Error("Input must be an array");
+  }
+
+  return array.reduce((acc, item) => {
+    acc[item] = (acc[item] ?? 0) + 1;
+    return acc;
+  }, {});
+}
+
+// Handle invalid cases
+const INVALID_CASES = [["hello", "Input must be an array"]];
+
+const printInvalidCases = () => {
+  for (const [data, expectedMessage] of INVALID_CASES) {
+    try {
+      tally(data);
+      console.log(`Unexpected success for ${JSON.stringify(data)}`);
+    } catch (error) {
+      console.log("-".repeat(50));
+      console.log(
+        `Data: ${JSON.stringify(data)}\nExpected: ${expectedMessage}\nReceived: ${error.message}`
+      );
+    }
+  }
+};
+
+if (require.main === module) {
+  console.log("ERROR MESSAGES");
+  printInvalidCases();
+  console.log("-".repeat(50));
+}
 
 module.exports = tally;

From 23e876b89a2a26b3fff7c397425a512c3628e22f Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Wed, 15 Jul 2026 23:59:10 +0100
Subject: [PATCH 14/18] update trim method in querystring.js

---
 Sprint-2/implement/querystring.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 39e232015..c9fd781a7 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -9,8 +9,8 @@ function parseQueryString(queryString) {
     if (pair === "") continue;
 
     const [keyPart, ...valueParts] = pair.split("=");
-    const rawKey = keyPart.trim("").replace(/\+/g, " ");
-    const rawValue = valueParts.join("=").trim("").replace(/\+/g, " ");
+    const rawKey = keyPart.trim().replace(/\+/g, " ");
+    const rawValue = valueParts.join("=").trim().replace(/\+/g, " ");
     const key = decodeURIComponent(rawKey);
     const value = decodeURIComponent(rawValue);
 

From 7e095824397e52f5e97d25a93e6f97a3daae0f4f Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 16 Jul 2026 15:43:59 +0100
Subject: [PATCH 15/18] fix issue in invert.js

---
 Sprint-2/interpret/invert.js | 80 +++++++++++++++++++++++++++++++++---
 1 file changed, 74 insertions(+), 6 deletions(-)

diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..3830725fc 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -7,23 +7,91 @@
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
 function invert(obj) {
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    throw new Error("Input must be an object");
+  }
+
+  if (Object.keys(obj).length === 0) {
+    return {};
+  }
+
   const invertedObj = {};
+  const seenValues = new Set();
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    const isKeyValid = typeof key === "string" || typeof key === "number";
+    const isValueValid = typeof value === "string" || typeof value === "number";
+
+    if (!isKeyValid || !isValueValid) {
+      throw new Error("Keys and values must be a string or a number");
+    }
+
+    if (seenValues.has(value)) {
+      throw new Error("Values cannot be duplicated");
+    }
+
+    seenValues.add(value);
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+// Handle invalid cases
+const INVALID_CASES = [
+  [{ a: {} }, "Keys and values must be a string or a number"],
+  [{ a: 1, b: 1 }, "Values cannot be duplicated"],
+  ["hello", "Input must be an object"],
+];
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
+const printInvalidCases = () => {
+  for (const [data, expectedMessage] of INVALID_CASES) {
+    try {
+      invert(data);
+      console.log(`Unexpected success for ${JSON.stringify(data)}`);
+    } catch (error) {
+      console.log("-".repeat(50));
+      console.log(
+        `Data: ${JSON.stringify(data)}\nExpected: ${expectedMessage}\nReceived: ${error.message}`
+      );
+    }
+  }
+};
 
-// c) What is the target return value when invert is called with {a : 1, b: 2}
+if (require.main === module) {
+  console.log("ERROR MESSAGES");
+  printInvalidCases();
+  console.log("-".repeat(50));
 
-// c) What does Object.entries return? Why is it needed in this program?
+  const runExample = (input) => {
+    try {
+      const result = invert(input);
+      console.log(
+        `Input: ${JSON.stringify(input)} => ${JSON.stringify(result)}`
+      );
+    } catch (error) {
+      console.log(`Input: ${JSON.stringify(input)} => ${error.message}`);
+    }
+  };
 
-// d) Explain why the current return value is different from the target output
+  // Example cases
+  runExample({ x: 10, x: 20 });
+  runExample({ a: 1 });
+  // Invalid cases
+  runExample({ x: 20, y: 20 });
+  runExample({ a: {} });
+}
+
+module.exports = invert;
 
+// a) What is the current return value when invert is called with { a : 1 }
+// Current return value is {key: 1}
+// b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Current return value is {key: 1, key: 2}
+// c) What is the target return value when invert is called with {a : 1, b: 2}
+// Target return value when invert is called with {a : 1, b: 2} is {key: 1, key: 2}
+// c) What does Object.entries return? Why is it needed in this program?
+// Object.entries returns the key / value pairs in nested arrays [["a", 1], "b", 2]].  It is needed in order for this programme to be able to work as it requires swapping of keys and values
+// d) Explain why the current return value is different from the target output
+// The current value is returning a key because it is using the key notation (invertedObj.key). It needs to be returned using brackets and the value and key swapped - inveretedObj[value] = key
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

From 253201d7843113998e7db3ee005f55cac235561f Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 16 Jul 2026 15:50:36 +0100
Subject: [PATCH 16/18] create test file invert.test.js - all tests pass

---
 Sprint-2/interpret/invert.test.js | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 Sprint-2/interpret/invert.test.js

diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..cd226a392
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,27 @@
+const invert = require("./invert");
+
+test("inverts valid keys and values", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+});
+
+test("inverts last key if keys are duplicated", () => {
+  expect(invert({ x: 10, x: 20 })).toEqual({ 20: "x" });
+});
+
+test("returns empty object if no input is provided", () => {
+  expect(invert({ x: 10, x: 20 })).toEqual({ 20: "x" });
+});
+
+test("throws when input is not an object", () => {
+  expect(() => invert("hello")).toThrow("Input must be an object");
+});
+
+test("throws when keys or values are not a string or number", () => {
+  expect(() => invert({ a: {} })).toThrow(
+    "Keys and values must be a string or a number"
+  );
+});
+
+test("throws when values are duplicated", () => {
+  expect(() => invert({ a: 1, b: 1 })).toThrow("Values cannot be duplicated");
+});

From 8a80a2027af635c338c8beb689a66dfe08f38a53 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Thu, 16 Jul 2026 15:57:29 +0100
Subject: [PATCH 17/18] Update empty object test in invert.test.js

---
 Sprint-2/interpret/invert.test.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
index cd226a392..dbec876a2 100644
--- a/Sprint-2/interpret/invert.test.js
+++ b/Sprint-2/interpret/invert.test.js
@@ -8,8 +8,8 @@ test("inverts last key if keys are duplicated", () => {
   expect(invert({ x: 10, x: 20 })).toEqual({ 20: "x" });
 });
 
-test("returns empty object if no input is provided", () => {
-  expect(invert({ x: 10, x: 20 })).toEqual({ 20: "x" });
+test("returns empty object if input has no keys", () => {
+  expect(invert({})).toEqual({});
 });
 
 test("throws when input is not an object", () => {

From 853d45b7653953a4d5088993d68c762d4a5ddce1 Mon Sep 17 00:00:00 2001
From: Martin Mwaka <martinmwaka@hotmail.com>
Date: Fri, 17 Jul 2026 06:59:42 +0100
Subject: [PATCH 18/18] Fix bug on line 68 of lookup.test.js

---
 Sprint-2/implement/lookup.js      | 4 ++--
 Sprint-2/implement/lookup.test.js | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index 1c2ef44a0..e77b07032 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -25,7 +25,7 @@ const validateData = (data) => {
   }
   // check that input is not empty
   if (data.length === 0) {
-    throw new Error("Input must not be empty");
+    throw new Error("Input must not be an empty array");
   }
 
   // check that the values are valid
@@ -50,7 +50,7 @@ const validateData = (data) => {
 
 // Handle invalid cases
 const INVALID_CASES = [
-  [[], "Input must not be empty"],
+  [[], "Input must not be an empty array"],
   ["hello", "Input must be an array"],
   [[1, 2, 3], "Input must be valid text pairs"],
   [
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index a70de530b..ca73a4259 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -66,7 +66,7 @@ describe("createLookup", () => {
       "Input must not be duplicated",
     ],
   ])("%s", (_title, data, expecteMessage) => {
-    expect(() => createLookup(data).toThrow(expecteMessage));
+    expect(() => createLookup(data)).toThrow(expecteMessage);
   });
 
   test("throws when country code format is incorrect", () => {