diff --git a/4.student-exercises.js b/4.student-exercises.js
new file mode 100644
index 0000000..bd6619f
--- /dev/null
+++ b/4.student-exercises.js
@@ -0,0 +1,17 @@
+const getTrainersAndGymsAndPokemons = (gyms, trainers, pokemons) => {
+  // Your code here
+};
+
+const getPsychicTrainersAndGyms = (gyms, trainers, pokemons) => {
+  // Your code here
+};
+
+const getGymsWithPokemons = (gyms, trainers, pokemons, ...pokemonsToFind) => {
+  // Your code here
+};
+
+module.exports = {
+  getPsychicTrainersAndGyms,
+  getTrainersAndGymsAndPokemons,
+  getGymsWithPokemons
+};
diff --git a/4.student-exercises.test.js b/4.student-exercises.test.js
new file mode 100644
index 0000000..1d233b4
--- /dev/null
+++ b/4.student-exercises.test.js
@@ -0,0 +1,71 @@
+const pokemons = require("./pokeData");
+const trainers = require("./trainerData");
+const gyms = require("./gymData");
+
+const {
+  getPsychicTrainersAndGyms,
+  getTrainersAndGymsAndPokemons,
+  getGymsWithPokemons
+} = require("./4.student-exercises");
+
+test("getTrainersAndGymsAndPokemons", () => {
+  const trainersAndGymsAndPokemons = getTrainersAndGymsAndPokemons(
+    gyms,
+    trainers,
+    pokemons
+  );
+  expect(trainersAndGymsAndPokemons.length).toBe(9);
+  expect(trainersAndGymsAndPokemons.map(trainer => trainer.gym)).toEqual(
+    expect.any(Object)
+  );
+  expect(trainersAndGymsAndPokemons.map(trainer => trainer.pokemons)).toEqual(
+    expect.any(Array)
+  );
+});
+
+test(`getPsychicTrainersAndGyms: expect a list of trainers with psychic pokemons.
+    also include (all) their pokemons and their gym`, () => {
+  const result = getPsychicTrainersAndGyms(gyms, trainers, pokemons);
+  expect(result.length).toEqual(2);
+  expect(result[0].name).toBe("Sabrina");
+  expect(result[1].name).toBe("Misty");
+  expect(result[0].gym).toEqual(expect.any(Object));
+  expect(result[1].gym).toEqual(expect.any(Object));
+  expect(result[0].gym.city).toBe("Saffron City");
+  expect(result[1].gym.city).toBe("Cerulean City");
+  expect(result[0].pokemons).toEqual(expect.any(Array));
+  expect(result[1].pokemons).toEqual(expect.any(Array));
+  expect(result[0].pokemons.length).toBe(4);
+  expect(result[1].pokemons.length).toBe(2);
+});
+
+test("getGymsWithPokemons: expect a list of gyms where certain pokemons can be found", () => {
+  const result = getGymsWithPokemons(
+    gyms,
+    trainers,
+    pokemons,
+    "Gloom",
+    "Starmie"
+  );
+  result.forEach(pokemon => {
+    expect(pokemon).toEqual(
+      expect.objectContaining({
+        id: expect.any(Number),
+        name: expect.any(String),
+        trainers: expect.any(Array),
+        gyms: expect.any(Array)
+      })
+    );
+  });
+  expect(result.length).toEqual(2);
+  expect(result[0].trainers.length).toEqual(2);
+  expect(result[1].trainers.length).toEqual(1);
+  expect(result[0].trainers[0].name).toBe("Brock");
+  expect(result[0].trainers[1].name).toBe("Erika");
+  expect(result[1].trainers[0].name).toBe("Misty");
+  expect(result[0].gyms.length).toEqual(2);
+  expect(result[1].gyms.length).toEqual(1);
+  expect(result[0].gyms[0].city).toBe("Celadon City");
+  expect(result[0].gyms[1].city).toBe("Pewter City");
+  expect(result[1].gyms[0].city).toBe("Cerulean City");
+});
diff --git a/gymData.js b/gymData.js
index 2bda417..887fdf7 100644
--- a/gymData.js
+++ b/gymData.js
@@ -1,10 +1,10 @@
 module.exports = [
-    { id: 1, city: 'Saffron City', trainerId: 2 },
-    { id: 2, city: 'Fuchsia City', trainerId: 3 },
-    { id: 3, city: 'Cinnabar Island', trainerId: 5 },
-    { id: 4, city: 'Celadon City ', trainerId: 7 },
-    { id: 5, city: 'Cerulean City', trainerId: 8 },
-    { id: 6, city: 'Vermilion City', trainerId: 6 },
-    { id: 7, city: 'Pewter City', trainerId: 1 },
-    { id: 8, city: 'Viridian City', trainerId: 4 },
-]
\ No newline at end of file
+  { id: 1, city: "Saffron City", trainerId: 2 },
+  { id: 2, city: "Fuchsia City", trainerId: 3 },
+  { id: 3, city: "Cinnabar Island", trainerId: 5 },
+  { id: 4, city: "Celadon City", trainerId: 7 },
+  { id: 5, city: "Cerulean City", trainerId: 8 },
+  { id: 6, city: "Vermilion City", trainerId: 6 },
+  { id: 7, city: "Pewter City", trainerId: 1 },
+  { id: 8, city: "Viridian City", trainerId: 4 }
+];
diff --git a/package.json b/package.json
index 04a5cdc..5b5eb8f 100644
--- a/package.json
+++ b/package.json
@@ -1,17 +1,18 @@
 {
-    "name": "data-transformations",
-    "version": "1.0.0",
-    "description": "A set of exercises for the data transformation day",
-    "main": "index.js",
-    "scripts": {
-        "test": "jest --watch",
-        "exercise1": "jest 1.map-filter-find.test --watch",
-        "exercise2": "jest 2.reduce.test --watch",
-        "exercise3": "jest 3.data-mining.test --watch"
-    },
-    "author": "Codaisseur",
-    "license": "ISC",
-    "devDependencies": {
-        "jest": "^24.7.1"
-    }
-}
\ No newline at end of file
+  "name": "data-transformations",
+  "version": "1.0.0",
+  "description": "A set of exercises for the data transformation day",
+  "main": "index.js",
+  "scripts": {
+    "test": "jest --watch",
+    "exercise1": "jest 1.map-filter-find.test --watch",
+    "exercise2": "jest 2.reduce.test --watch",
+    "exercise3": "jest 3.data-mining.test --watch",
+    "exercise4": "jest 4.student-exercises.test --watch"
+  },
+  "author": "Codaisseur",
+  "license": "ISC",
+  "devDependencies": {
+    "jest": "^24.7.1"
+  }
+}
diff --git a/trainerData.js b/trainerData.js
index bf27fd2..152bb1d 100644
--- a/trainerData.js
+++ b/trainerData.js
@@ -1,11 +1,11 @@
 module.exports = [
-    { id: 1, name: 'Brock', pokemonIds: [74, 95] },
-    { id: 2, name: 'Sabrina', pokemonIds: [64, 122, 49, 65] },
-    { id: 3, name: 'Koga', pokemonIds: [109, 110, 109, 89] },
-    { id: 4, name: 'Giovanni', pokemonIds: [112, 51, 31, 34, 113] },
-    { id: 5, name: 'Blaine', pokemonIds: [58, 77, 78, 59] },
-    { id: 6, name: 'Lt. Surge', pokemonIds: [100, 25, 26] },
-    { id: 7, name: 'Erika', pokemonIds: [71, 114, 44] },
-    { id: 8, name: 'Misty', pokemonIds: [120, 121] },
-    { id: 9, name: 'Ash', pokemonIds: [25, 1, 7, 6, 17, 12] },
-]
\ No newline at end of file
+  { id: 1, name: "Brock", pokemonIds: [74, 95, 44] },
+  { id: 2, name: "Sabrina", pokemonIds: [64, 122, 49, 65] },
+  { id: 3, name: "Koga", pokemonIds: [109, 110, 109, 89] },
+  { id: 4, name: "Giovanni", pokemonIds: [112, 51, 31, 34, 113] },
+  { id: 5, name: "Blaine", pokemonIds: [58, 77, 78, 59] },
+  { id: 6, name: "Lt. Surge", pokemonIds: [100, 25, 26] },
+  { id: 7, name: "Erika", pokemonIds: [71, 114, 44] },
+  { id: 8, name: "Misty", pokemonIds: [120, 121] },
+  { id: 9, name: "Ash", pokemonIds: [25, 1, 7, 6, 17, 12] }
+];