diff --git a/Gemfile b/Gemfile
index f3137b7..0cf4a1b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -51,6 +51,7 @@ group :development, :test do
   gem "rubocop-rails-omakase", require: false
 
   gem "rspec-rails", "~> 8.0.0"
+  gem "factory_bot_rails"
 end
 
 group :development do
diff --git a/Gemfile.lock b/Gemfile.lock
index 3e09b30..901d9aa 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -113,6 +113,11 @@ GEM
     erubi (1.13.1)
     et-orbi (1.2.11)
       tzinfo
+    factory_bot (6.5.6)
+      activesupport (>= 6.1.0)
+    factory_bot_rails (6.5.1)
+      factory_bot (~> 6.5)
+      railties (>= 6.1.0)
     fugit (1.11.1)
       et-orbi (~> 1, >= 1.2.11)
       raabro (~> 1.4)
@@ -435,6 +440,7 @@ DEPENDENCIES
   capybara
   cssbundling-rails (~> 1.4)
   debug
+  factory_bot_rails
   haml
   importmap-rails
   jbuilder
diff --git a/spec/factories/moods.rb b/spec/factories/moods.rb
new file mode 100644
index 0000000..e75d860
--- /dev/null
+++ b/spec/factories/moods.rb
@@ -0,0 +1,7 @@
+FactoryBot.define do
+  factory :mood do
+    mode { "croisiere" }
+    recorded_at { DateTime.now }
+    association :user
+  end
+end
diff --git a/spec/factories/user.rb b/spec/factories/user.rb
new file mode 100644
index 0000000..26f4019
--- /dev/null
+++ b/spec/factories/user.rb
@@ -0,0 +1,6 @@
+FactoryBot.define do
+  factory :user do
+    sequence(:email_address) { |n| "user#{n}@example.com" }
+    password_digest { BCrypt::Password.create('password123') }
+  end
+end
diff --git a/spec/rails_helper.rb b/spec/rails_helper.rb
index 79811b8..b972cd2 100644
--- a/spec/rails_helper.rb
+++ b/spec/rails_helper.rb
@@ -9,21 +9,23 @@ abort("The Rails environment is running in production mode!") if Rails.env.produ
 # return unless Rails.env.test?
 require 'rspec/rails'
 # Add additional requires below this line. Rails is not loaded until this point!
+require 'factory_bot_rails'
 
-# Requires supporting ruby files with custom matchers and macros, etc, in
-# spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
-# run as spec files by default. This means that files in spec/support that end
-# in _spec.rb will both be required and run as specs, causing the specs to be
-# run twice. It is recommended that you do not name files matching this glob to
-# end with _spec.rb. You can configure this pattern with the --pattern
-# option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
-#
-# The following line is provided for convenience purposes. It has the downside
-# of increasing the boot-up time by auto-requiring all files in the support
-# directory. Alternatively, in the individual `*_spec.rb` files, manually
-# require only the support files necessary.
-#
-# Rails.root.glob('spec/support/**/*.rb').sort_by(&:to_s).each { |f| require f }
+ # Requires supporting ruby files with custom matchers and macros, etc, in
+ # spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
+ # run as spec files by default. This means that files in spec/support that end
+ # in _spec.rb will both be required and run as specs, causing the specs to be
+ # run twice. It is recommended that you do not name files matching this glob to
+ # end with _spec.rb. You can configure this pattern with the --pattern
+ # option on the command line or in ~/.rspec, .rspec or `.rspec-local`.
+ #
+ # The following line is provided for convenience purposes. It has the downside
+ # of increasing the boot-up time by auto-requiring all files in the support
+ # directory. Alternatively, in the individual `*_spec.rb` files, manually
+ # require only the support files necessary.
+ #
+ # Rails.root.glob('spec/support/**/*.rb').sort_by(&:to_s).each { |f| require f }
+ Rails.root.glob('spec/support/**/*.rb').sort_by(&:to_s).each { |f| require f }
 
 # Ensures that the test database schema matches the current schema file.
 # If there are pending migrations it will invoke `db:test:prepare` to
diff --git a/spec/services/mood_calendar_service_spec.rb b/spec/services/mood_calendar_service_spec.rb
new file mode 100644
index 0000000..5cc4a55
--- /dev/null
+++ b/spec/services/mood_calendar_service_spec.rb
@@ -0,0 +1,422 @@
+# spec/services/mood_calendar_service_spec.rb
+require 'rails_helper'
+
+RSpec.describe MoodCalendarService do
+  describe '.generate_calendar' do
+    context 'avec un recorded_at pour chaque jour' do
+      it 'génère un calendrier complet sans jours nil' do
+        # Données du 1er au 7 février 2025 (une semaine complète)
+        (1..7).each do |day|
+          create(:mood, mode: "mood_#{day}", recorded_at: Time.zone.parse("2025-02-0#{day} 10:00:00"))
+        end
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        expect(result.length).to eq(1) # Un seul mois
+        expect(result[0][:month]).to eq(Date.parse("2025-02-01"))
+        
+        # Première semaine commence le lundi 3 février
+        first_week = result[0][:weeks][0]
+        expect(first_week.length).to eq(7) # Du lundi 3 au dimanche 9
+        
+        # Vérifier que tous les jours du 3 au 7 ont un mode
+        (3..7).each do |day|
+          mood = first_week.find { |m| m[:recorded_at].day == day }
+          expect(mood[:mode]).to eq("mood_#{day}")
+          expect(mood).not_to have_key(:guess)
+        end
+        
+        # Le 8 et 9 février devraient avoir mode: nil avec guess: "mood_7"
+        mood_8 = first_week.find { |m| m[:recorded_at].day == 8 }
+        expect(mood_8[:mode]).to be_nil
+        expect(mood_8[:guess]).to eq("mood_7")
+        
+        mood_9 = first_week.find { |m| m[:recorded_at].day == 9 }
+        expect(mood_9[:mode]).to be_nil
+        expect(mood_9[:guess]).to eq("mood_7")
+      end
+    end
+
+    context 'avec des jours manquants' do
+      it 'remplit les jours manquants avec mode: nil et guess égal au dernier mode' do
+        create(:mood, mode: "triste", recorded_at: Time.zone.parse("2025-02-12 08:30:00"))
+        create(:mood, mode: "content", recorded_at: Time.zone.parse("2025-02-12 14:20:00"))
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+        create(:mood, mode: "calme", recorded_at: Time.zone.parse("2025-02-18 16:45:00"))
+
+        moods = Mood.all
+        result = MoodCalendarService.generate_calendar(
+          moods,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        expect(result.length).to eq(1)
+        expect(result[0][:month]).to eq(Date.parse("2025-02-01"))
+        
+        # Trouver tous les jours
+        all_days = result[0][:weeks].flatten
+        
+        # Le 12 février devrait avoir le dernier mood (content à 14:20)
+        mood_12 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-12") }
+        expect(mood_12[:mode]).to eq("content")
+        expect(mood_12[:recorded_at].to_i).to eq(Time.zone.parse("2025-02-12 14:20:00").to_i)
+        
+        # Le 13 février devrait être nil avec guess: "content"
+        mood_13 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-13") }
+        expect(mood_13[:mode]).to be_nil
+        expect(mood_13[:guess]).to eq("content")
+        
+        # Le 14 février devrait être nil avec guess: "content"
+        mood_14 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-14") }
+        expect(mood_14[:mode]).to be_nil
+        expect(mood_14[:guess]).to eq("content")
+        
+        # Le 15 février devrait avoir le mood "heureux"
+        mood_15 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-15") }
+        expect(mood_15[:mode]).to eq("heureux")
+        
+        # Le 16 février devrait être nil avec guess: "heureux"
+        mood_16 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-16") }
+        expect(mood_16[:mode]).to be_nil
+        expect(mood_16[:guess]).to eq("heureux")
+        
+        # Les jours avant le 12 (à partir du premier lundi 3 février) devraient avoir guess: nil
+        mood_3 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-03") }
+        expect(mood_3[:mode]).to be_nil
+        expect(mood_3[:guess]).to be_nil
+      end
+
+      it 'gère correctement plusieurs mois avec des jours manquants' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+        create(:mood, mode: "joyeux", recorded_at: Time.zone.parse("2025-04-20 11:30:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-04-30")
+        )
+
+        # Devrait avoir exactement février, mars et avril
+        expect(result.length).to eq(3)
+        
+        # Vérifier février
+        february = result.find { |m| m[:month] == Date.parse("2025-02-01") }
+        expect(february).not_to be_nil
+        
+        # Vérifier mars (tous les jours devraient avoir mode: nil et guess: "heureux")
+        march = result.find { |m| m[:month] == Date.parse("2025-03-01") }
+        expect(march).not_to be_nil
+        all_march_days = march[:weeks].flatten
+        
+        # Tous les jours de mars (y compris ceux qui débordent début avril) devraient avoir mode: nil
+        expect(all_march_days.all? { |d| d[:mode].nil? }).to be true
+        
+        # Tous les jours de mars devraient avoir guess: "heureux"
+        # (le mois de mars va du 3 mars au 6 avril, avant le mood du 20 avril)
+        all_march_days.each do |day|
+          expect(day[:guess]).to eq("heureux"), 
+            "Le jour #{day[:recorded_at].to_date} devrait avoir guess: 'heureux' mais a: #{day[:guess].inspect}"
+        end
+        
+        # Vérifier avril
+        april = result.find { |m| m[:month] == Date.parse("2025-04-01") }
+        expect(april).not_to be_nil
+        all_april_days = april[:weeks].flatten
+        mood_20_april = all_april_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-04-20") }
+        expect(mood_20_april[:mode]).to eq("joyeux")
+        
+        # Les jours du 7 au 19 avril devraient avoir guess: "heureux"
+        mood_10_april = all_april_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-04-10") }
+        expect(mood_10_april[:guess]).to eq("heureux")
+        
+        # Les jours après le 20 avril devraient avoir guess: "joyeux"
+        mood_21_april = all_april_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-04-21") }
+        expect(mood_21_april[:guess]).to eq("joyeux")
+      end
+    end
+
+    context 'sans aucun recorded_at' do
+      it 'retourne un tableau vide' do
+        result = MoodCalendarService.generate_calendar(Mood.none)
+
+        expect(result).to eq([])
+      end
+    end
+
+    context 'avec plusieurs moods le même jour' do
+      it 'garde uniquement le mood le plus récent' do
+        create(:mood, mode: "triste", recorded_at: Time.zone.parse("2025-02-12 08:30:00"))
+        create(:mood, mode: "neutre", recorded_at: Time.zone.parse("2025-02-12 12:00:00"))
+        create(:mood, mode: "content", recorded_at: Time.zone.parse("2025-02-12 14:20:00"))
+        create(:mood, mode: "fatigué", recorded_at: Time.zone.parse("2025-02-12 09:15:00"))
+
+        moods = Mood.all
+        result = MoodCalendarService.generate_calendar(
+          moods,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        all_days = result[0][:weeks].flatten
+        mood_12 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-12") }
+        
+        expect(mood_12[:mode]).to eq("content")
+        expect(mood_12[:recorded_at].to_i).to eq(Time.zone.parse("2025-02-12 14:20:00").to_i)
+      end
+    end
+
+    context 'structure du calendrier' do
+      it 'commence chaque mois par le premier lundi' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        february = result[0]
+        first_day = february[:weeks][0][0]
+        
+        # Le premier jour de février 2025 devrait être le lundi 3 février
+        expect(first_day[:recorded_at].to_date).to eq(Date.parse("2025-02-03"))
+        expect(first_day[:recorded_at].to_date.monday?).to be true
+      end
+
+      it 'va du premier lundi du mois au dimanche avant le premier lundi du mois suivant' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-03-31")
+        )
+
+        february = result[0]
+        all_days = february[:weeks].flatten
+        
+        # Premier jour : lundi 3 février 2025
+        first_day = all_days.first
+        expect(first_day[:recorded_at].to_date).to eq(Date.parse("2025-02-03"))
+        expect(first_day[:recorded_at].to_date.monday?).to be true
+        
+        # Dernier jour : dimanche 2 mars 2025 (veille du premier lundi de mars qui est le 3)
+        last_day = all_days.last
+        expect(last_day[:recorded_at].to_date).to eq(Date.parse("2025-03-02"))
+        expect(last_day[:recorded_at].to_date.sunday?).to be true
+        
+        # Le 3 mars (premier lundi de mars) ne devrait PAS être dans février
+        expect(all_days.any? { |d| d[:recorded_at].to_date == Date.parse("2025-03-03") }).to be false
+      end
+
+      it 'toutes les semaines ont exactement 7 jours' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        february = result[0]
+        
+        # Toutes les semaines devraient avoir exactement 7 jours
+        february[:weeks].each do |week|
+          expect(week.length).to eq(7)
+        end
+      end
+
+      it 'retourne month comme Date (le premier du mois)' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        february = result[0]
+        
+        # month devrait être une Date
+        expect(february[:month]).to be_a(Date)
+        expect(february[:month]).to eq(Date.parse("2025-02-01"))
+        expect(february[:month].day).to eq(1) # Premier du mois
+      end
+    end
+
+    context 'avec paramètres par défaut' do
+      it 'utilise le premier mood comme start_date et aujourd\'hui comme end_date' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(Mood.all)
+
+        expect(result).not_to be_empty
+        
+        # Devrait commencer en février
+        expect(result.first[:month]).to eq(Date.parse("2025-02-01"))
+      end
+    end
+
+    context 'avec start_date spécifié' do
+      it 'commence à la date spécifiée' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          start_date: Date.parse("2025-03-01"),
+          end_date: Date.parse("2025-03-31")
+        )
+
+        # Devrait commencer en mars même si le mood est en février
+        expect(result.first[:month]).to eq(Date.parse("2025-03-01"))
+        
+        # Ne devrait pas contenir février
+        expect(result.any? { |m| m[:month] == Date.parse("2025-02-01") }).to be false
+        
+        # Tous les jours de mars devraient avoir guess: "heureux" (du 15 février)
+        all_march_days = result.first[:weeks].flatten
+        puts all_march_days.inspect
+        expect(all_march_days.all? { |d| d[:guess] == "heureux" }).to be true
+      end
+    end
+
+    context 'avec end_date spécifié' do
+      it 'se termine à la date spécifiée' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        # Devrait s'arrêter en février
+        expect(result.last[:month]).to eq(Date.parse("2025-02-01"))
+        
+        # Ne devrait pas contenir mars ou au-delà
+        expect(result.any? { |m| m[:month] == Date.parse("2025-03-01") }).to be false
+      end
+    end
+
+    context 'avec start_date et end_date spécifiés' do
+      it 'génère le calendrier pour la plage spécifiée' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+        create(:mood, mode: "calme", recorded_at: Time.zone.parse("2025-04-20 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          start_date: Date.parse("2025-03-01"),
+          end_date: Date.parse("2025-03-31")
+        )
+
+        # Devrait contenir uniquement mars
+        expect(result.length).to eq(1)
+        expect(result.first[:month]).to eq(Date.parse("2025-03-01"))
+        
+        # Tous les jours de mars devraient avoir guess: "heureux" (du 15 février)
+        all_days = result.first[:weeks].flatten
+        expect(all_days.all? { |d| d[:mode].nil? }).to be true
+        expect(all_days.all? { |d| d[:guess] == "heureux" }).to be true
+      end
+
+      it 'gère une plage de plusieurs mois' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          start_date: Date.parse("2025-02-01"),
+          end_date: Date.parse("2025-04-30")
+        )
+
+        # Devrait contenir février, mars et avril
+        months = result.map { |m| m[:month] }
+        expect(months).to include(
+          Date.parse("2025-02-01"),
+          Date.parse("2025-03-01"),
+          Date.parse("2025-04-01")
+        )
+      end
+
+      it 'fonctionne avec DateTime en paramètres' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        # Passer des DateTime au lieu de Date
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          start_date: Time.zone.parse("2025-02-01 00:00:00"),
+          end_date: Time.zone.parse("2025-02-28 23:59:59")
+        )
+
+        expect(result).not_to be_empty
+        expect(result.first[:month]).to eq(Date.parse("2025-02-01"))
+      end
+    end
+
+    context 'avec une plage ne contenant aucun mood' do
+      it 'génère un calendrier avec tous les jours à nil et guess du dernier mood avant la plage' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          start_date: Date.parse("2025-04-01"),
+          end_date: Date.parse("2025-04-30")
+        )
+
+        # Devrait contenir avril
+        expect(result.first[:month]).to eq(Date.parse("2025-04-01"))
+        
+        # Tous les jours devraient avoir mode: nil et guess: "heureux"
+        all_days = result.first[:weeks].flatten
+        expect(all_days.all? { |d| d[:mode].nil? }).to be true
+        expect(all_days.all? { |d| d[:guess] == "heureux" }).to be true
+      end
+    end
+
+    context 'avec plusieurs mois' do
+      it 'chaque mois commence et finit correctement' do
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"))
+        create(:mood, mode: "calme", recorded_at: Time.zone.parse("2025-03-20 10:00:00"))
+
+        result = MoodCalendarService.generate_calendar(
+          Mood.all,
+          end_date: Date.parse("2025-03-31")
+        )
+
+        february = result.find { |m| m[:month] == Date.parse("2025-02-01") }
+        march = result.find { |m| m[:month] == Date.parse("2025-03-01") }
+        
+        # Février se termine le dimanche 2 mars
+        last_day_february = february[:weeks].flatten.last
+        expect(last_day_february[:recorded_at].to_date).to eq(Date.parse("2025-03-02"))
+        
+        # Mars commence le lundi 3 mars
+        first_day_march = march[:weeks].flatten.first
+        expect(first_day_march[:recorded_at].to_date).to eq(Date.parse("2025-03-03"))
+        
+        # Pas de chevauchement
+        expect(last_day_february[:recorded_at].to_date + 1.day).to eq(first_day_march[:recorded_at].to_date)
+      end
+    end
+
+    context 'avec un scope spécifique' do
+      it 'fonctionne avec des moods filtrés par user' do
+        user1 = create(:user)
+        user2 = create(:user)
+        
+        create(:mood, mode: "heureux", recorded_at: Time.zone.parse("2025-02-15 10:00:00"), user: user1)
+        create(:mood, mode: "triste", recorded_at: Time.zone.parse("2025-02-16 10:00:00"), user: user2)
+
+        moods = Mood.where(user: user1)
+        result = MoodCalendarService.generate_calendar(
+          moods,
+          end_date: Date.parse("2025-02-28")
+        )
+
+        all_days = result[0][:weeks].flatten
+        mood_15 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-15") }
+        expect(mood_15[:mode]).to eq("heureux")
+        
+        # Le mood du user2 ne devrait pas apparaître
+        mood_16 = all_days.find { |m| m[:recorded_at].to_date == Date.parse("2025-02-16") }
+        expect(mood_16[:mode]).to be_nil
+        expect(mood_16[:guess]).to eq("heureux")
+      end
+    end
+  end
+end
diff --git a/spec/support/factory_bot.rb b/spec/support/factory_bot.rb
new file mode 100644
index 0000000..c7890e4
--- /dev/null
+++ b/spec/support/factory_bot.rb
@@ -0,0 +1,3 @@
+RSpec.configure do |config|
+  config.include FactoryBot::Syntax::Methods
+end