diff --git a/README.md b/README.md
index 2fa0341..d8f90bc 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# turniere-backend [![pipeline status](https://gitlab.com/turniere/turniere-backend/badges/master/pipeline.svg)](https://gitlab.com/turniere/turniere-backend/commits/master) [![Coverage Status](https://coveralls.io/repos/gitlab/turniere/turniere-backend/badge.svg?branch=ticket%2FTURNIERE-155)](https://coveralls.io/gitlab/turniere/turniere-backend?branch=ticket%2FTURNIERE-155)
+# turniere-backend [![Build Status](https://travis-ci.org/turniere/turniere-backend.svg?branch=master)](https://travis-ci.org/turniere/turniere-backend) [![pipeline status](https://gitlab.com/turniere/turniere-backend/badges/master/pipeline.svg)](https://gitlab.com/turniere/turniere-backend/commits/master) [![Coverage Status](https://coveralls.io/repos/gitlab/turniere/turniere-backend/badge.svg?branch=master)](https://coveralls.io/gitlab/turniere/turniere-backend?branch=master) [![](https://img.shields.io/badge/Protected_by-Hound-a873d1.svg)](https://houndci.com)
 Ruby on Rails application serving as backend for turnie.re
 
 # Installation
diff --git a/app/controllers/tournaments_controller.rb b/app/controllers/tournaments_controller.rb
index e8ea5c0..6a4a3e5 100644
--- a/app/controllers/tournaments_controller.rb
+++ b/app/controllers/tournaments_controller.rb
@@ -31,25 +31,27 @@ class TournamentsController < ApplicationController
   def create
     params = tournament_params
     params.require(:teams)
-    # convert teams parameter into Team objects
-    teams = params.delete('teams').map do |team|
-      if team[:id]
-        Team.find team[:id]
-      elsif team[:name]
-        Team.create name: team[:name]
-      end
-    end
+    group_stage = params.delete(:group_stage)
+    teams = params.delete('teams')
     # create tournament
     tournament = current_user.tournaments.new params
-    # associate provided teams with tournament
-    tournament.teams = teams
+    if group_stage
+      groups = organize_teams_in_groups(teams)
+      # add groups to tournament
+      result = AddGroupStageToTournamentAndSaveTournamentToDatabase.call(tournament: tournament, groups: groups)
+    else
+      # convert teams parameter into Team objects
+      teams = teams.map(&method(:find_or_create_team))
+      # associate provided teams with tournament
+      tournament.teams = teams
+      # add playoff stage to tournament
+      result = AddPlayoffsToTournamentAndSaveTournamentToDatabase.call(tournament: tournament)
+    end
     # validate tournament
     unless tournament.valid?
       render json: tournament.errors, status: :unprocessable_entity
       return
     end
-    # add playoff stage to tournament
-    result = AddPlayoffsToTournamentAndSaveTournamentToDatabase.call(tournament: tournament)
     # return appropriate result
     if result.success?
       render json: result.tournament, status: :created, location: result.tournament
@@ -74,6 +76,24 @@ class TournamentsController < ApplicationController
 
   private
 
+  def organize_teams_in_groups(teams)
+    # each team gets put into a array of teams depending on the group specified in team[:group]
+    teams.group_by { |team| team['group'] }.values.map do |group|
+      group.map do |team|
+        find_or_create_team(team)
+      end
+    end
+  end
+
+  def find_or_create_team(team)
+    # convert teams parameter into Team objects
+    if team[:id]
+      Team.find team[:id]
+    elsif team[:name]
+      Team.create name: team[:name]
+    end
+  end
+
   def set_tournament
     @tournament = Tournament.find(params[:id])
   end
@@ -83,7 +103,7 @@ class TournamentsController < ApplicationController
   end
 
   def tournament_params
-    params.slice(:name, :description, :public, :teams).permit!
+    params.slice(:name, :description, :public, :teams, :group_stage).permit!
   end
 
   def validate_create_params
diff --git a/app/interactors/add_group_stage_to_tournament.rb b/app/interactors/add_group_stage_to_tournament.rb
new file mode 100644
index 0000000..14b798c
--- /dev/null
+++ b/app/interactors/add_group_stage_to_tournament.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class AddGroupStageToTournament
+  include Interactor
+
+  def call
+    tournament = context.tournament
+    groups = context.groups
+    context.fail! unless tournament.stages.empty?
+    begin
+      group_stage = GroupStageService.generate_group_stage(groups)
+      tournament.stages = [group_stage]
+      context.tournament = tournament
+    rescue StandardError
+      context.fail!
+    end
+  end
+end
diff --git a/app/models/group.rb b/app/models/group.rb
index 39cba55..1b99378 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -4,4 +4,8 @@ class Group < ApplicationRecord
   belongs_to :stage
   has_many :matches, dependent: :destroy
   has_many :group_scores, dependent: :destroy
+
+  def teams
+    matches.map(&:teams).flatten.uniq
+  end
 end
diff --git a/app/models/match.rb b/app/models/match.rb
index 0eb0c14..6c3eee8 100644
--- a/app/models/match.rb
+++ b/app/models/match.rb
@@ -11,6 +11,10 @@ class Match < ApplicationRecord
 
   validate :stage_xor_group
 
+  def teams
+    match_scores.map(&:team).flatten.uniq
+  end
+
   private
 
   def stage_xor_group
diff --git a/app/models/stage.rb b/app/models/stage.rb
index b43d80c..48ad20d 100644
--- a/app/models/stage.rb
+++ b/app/models/stage.rb
@@ -4,4 +4,10 @@ class Stage < ApplicationRecord
   belongs_to :tournament
   has_many :matches, dependent: :destroy
   has_many :groups, dependent: :destroy
+
+  def teams
+    return matches.map(&:teams).flatten.uniq unless matches.size.zero?
+
+    groups.map(&:teams).flatten.uniq unless groups.size.zero?
+  end
 end
diff --git a/app/organizers/add_group_stage_to_tournament_and_save_tournament_to_database.rb b/app/organizers/add_group_stage_to_tournament_and_save_tournament_to_database.rb
new file mode 100644
index 0000000..83710b5
--- /dev/null
+++ b/app/organizers/add_group_stage_to_tournament_and_save_tournament_to_database.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddGroupStageToTournamentAndSaveTournamentToDatabase
+  include Interactor::Organizer
+
+  organize AddGroupStageToTournament, SaveTournamentToDatabase
+end
diff --git a/app/services/group_stage_service.rb b/app/services/group_stage_service.rb
new file mode 100644
index 0000000..ea03168
--- /dev/null
+++ b/app/services/group_stage_service.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class GroupStageService
+  def self.generate_group_stage(groups)
+    raise 'Cannot generate group stage without groups' if groups.length.zero?
+
+    # raise an error if the average group size is not a whole number
+    raise 'Groups need to be equal size' unless (groups.flatten.length.to_f / groups.length.to_f % 1).zero?
+
+    groups = groups.map(&method(:get_group_object_from))
+    Stage.new level: -1, groups: groups
+  end
+
+  def self.get_group_object_from(team_array)
+    Group.new matches: generate_all_matches_between(team_array)
+  end
+
+  def self.generate_all_matches_between(teams)
+    matches = []
+    teams.combination(2).to_a # = matchups
+         .each_with_index do |matchup, i|
+      match = Match.new state: :not_started,
+                        position: i,
+                        match_scores: [
+                          MatchScore.new(team: matchup.first),
+                          MatchScore.new(team: matchup.second)
+                        ]
+      matches << match
+    end
+    matches
+  end
+end
diff --git a/spec/controllers/tournaments_controller_spec.rb b/spec/controllers/tournaments_controller_spec.rb
index 7dc9d2e..da27ca7 100644
--- a/spec/controllers/tournaments_controller_spec.rb
+++ b/spec/controllers/tournaments_controller_spec.rb
@@ -9,6 +9,8 @@ RSpec.describe TournamentsController, type: :controller do
     @another_user = create(:user)
     @private_tournament = create(:tournament, user: @another_user, public: false)
     @teams = create_list(:detached_team, 4)
+    @teams16 = create_list(:detached_team, 16)
+    @groups = create_list(:group, 4)
   end
 
   describe 'GET #index' do
@@ -103,7 +105,7 @@ RSpec.describe TournamentsController, type: :controller do
   end
 
   describe 'POST #create' do
-    let(:create_data) do
+    let(:create_playoff_tournament_data) do
       {
         name: Faker::Creature::Dog.name,
         description: Faker::Lorem.sentence,
@@ -112,9 +114,20 @@ RSpec.describe TournamentsController, type: :controller do
       }
     end
 
+    let(:create_group_tournament_data) do
+      teams_with_groups = @teams16.each_with_index.map { |team, i| { id: team.id, group: (i / 4).floor } }
+      {
+        name: Faker::TvShows::FamilyGuy.character,
+        description: Faker::Movies::HarryPotter.quote,
+        public: false,
+        group_stage: true,
+        teams: teams_with_groups
+      }
+    end
+
     context 'without authentication headers' do
       it 'renders an unauthorized error response' do
-        put :create, params: create_data
+        put :create, params: create_playoff_tournament_data
         expect(response).to have_http_status(:unauthorized)
       end
     end
@@ -127,40 +140,58 @@ RSpec.describe TournamentsController, type: :controller do
       context 'with existing teams' do
         it 'creates a new Tournament' do
           expect do
-            post :create, params: create_data
+            post :create, params: create_playoff_tournament_data
           end.to change(Tournament, :count).by(1)
         end
 
         it 'associates the new tournament with the authenticated user' do
           expect do
-            post :create, params: create_data
+            post :create, params: create_playoff_tournament_data
           end.to change(@user.tournaments, :count).by(1)
         end
 
         it 'associates the given teams with the created tournament' do
-          post :create, params: create_data
+          post :create, params: create_playoff_tournament_data
           body = deserialize_response response
           tournament = Tournament.find(body[:id])
           expect(tournament.teams).to match_array(@teams)
         end
 
         it 'generates a playoff stage' do
-          post :create, params: create_data
+          post :create, params: create_playoff_tournament_data
           body = deserialize_response response
           tournament = Tournament.find(body[:id])
           expect(tournament.stages.first).to be_a(Stage)
         end
 
         it 'generates a playoff stage with all given teams' do
-          post :create, params: create_data
+          post :create, params: create_playoff_tournament_data
           body = deserialize_response response
           tournament = Tournament.find(body[:id])
           included_teams = tournament.stages.first.matches.map { |m| m.match_scores.map(&:team) }.flatten.uniq
           expect(included_teams).to match_array(@teams)
         end
 
+        context 'with parameter group_stage=true' do
+          before do
+            post :create, params: create_group_tournament_data
+            body = deserialize_response response
+            @group_stage_tournament = Tournament.find(body[:id])
+          end
+
+          it 'generates a group stage with all teams given in parameters' do
+            included_teams = @group_stage_tournament.stages.find_by(level: -1).teams
+            expect(included_teams).to match_array(@teams16)
+          end
+
+          it 'generates a group stage' do
+            group_stage = @group_stage_tournament.stages.find_by(level: -1)
+            expect(group_stage).to be_a(Stage)
+          end
+        end
+
         it 'renders a JSON response with the new tournament' do
-          post :create, params: create_data
+          post :create, params: create_playoff_tournament_data
           expect(response).to have_http_status(:created)
           expect(response.content_type).to eq('application/json')
           expect(response.location).to eq(tournament_url(Tournament.last))
@@ -169,16 +200,25 @@ RSpec.describe TournamentsController, type: :controller do
 
       context 'with missing teams' do
         it 'returns an error response' do
-          data = create_data
+          data = create_playoff_tournament_data
           data[:teams] << { id: Team.last.id + 1 }
           post :create, params: data
           expect(response).to have_http_status(:not_found)
         end
       end
 
+      context 'with unequal group sizes' do
+        it 'returns an error response' do
+          data = create_group_tournament_data
+          data[:teams].pop
+          post :create, params: data
+          expect(response).to have_http_status(:unprocessable_entity)
+        end
+      end
+
       context 'with team names' do
         it 'creates teams for given names' do
-          data = create_data
+          data = create_playoff_tournament_data
           data.delete :teams
           data[:teams] = (1..12).collect { { name: Faker::Creature::Dog.name } }
           expect do
@@ -193,6 +233,15 @@ RSpec.describe TournamentsController, type: :controller do
           expect(response).to have_http_status(:unprocessable_entity)
         end
       end
+
+      context 'with empty team objects' do
+        it 'renders an unprocessable entity response' do
+          data = create_group_tournament_data
+          data[:teams] = [{ group: 1 }, { group: 1 }, { group: 2 }, { group: 2 }]
+          post :create, params: data
+          expect(response).to have_http_status(:unprocessable_entity)
+        end
+      end
     end
   end
 
diff --git a/spec/factories/groups.rb b/spec/factories/groups.rb
index 841f741..839c230 100644
--- a/spec/factories/groups.rb
+++ b/spec/factories/groups.rb
@@ -2,7 +2,15 @@
 
 FactoryBot.define do
   factory :group do
-    number { 0 }
+    transient do
+      match_count { 4 }
+    end
+
+    sequence(:number)
     stage
+
+    after(:create) do |group, evaluator|
+      create_list(:group_match, evaluator.match_count, group: group)
+    end
   end
 end
diff --git a/spec/factories/matches.rb b/spec/factories/matches.rb
index 773151f..3f0a89c 100644
--- a/spec/factories/matches.rb
+++ b/spec/factories/matches.rb
@@ -16,5 +16,14 @@ FactoryBot.define do
 
   factory :group_match, class: Match do
     group
+    factory :running_group_match do
+      transient do
+        match_scores_count { 2 }
+      end
+      after(:create) do |match, evaluator|
+        match.match_scores = create_list(:match_score, evaluator.match_scores_count)
+      end
+      state { 3 }
+    end
   end
 end
diff --git a/spec/factories/stages.rb b/spec/factories/stages.rb
index 4353af1..e8dce2d 100644
--- a/spec/factories/stages.rb
+++ b/spec/factories/stages.rb
@@ -3,5 +3,24 @@
 FactoryBot.define do
   factory :stage do
     tournament
+    factory :group_stage do
+      level { -1 }
+      transient do
+        group_count { 4 }
+      end
+      after(:create) do |stage, evaluator|
+        stage.groups = create_list(:group, evaluator.group_count)
+      end
+    end
+
+    factory :playoff_stage do
+      level { rand(10) }
+      transient do
+        match_count { 4 }
+      end
+      after(:create) do |stage, evaluator|
+        stage.matches = create_list(:match, evaluator.match_count)
+      end
+    end
   end
 end
diff --git a/spec/factories/tournaments.rb b/spec/factories/tournaments.rb
index 4b93176..6924332 100644
--- a/spec/factories/tournaments.rb
+++ b/spec/factories/tournaments.rb
@@ -11,6 +11,7 @@ FactoryBot.define do
     after(:create) do |tournament, evaluator|
       tournament.teams = create_list(:team, evaluator.teams_count, tournament: tournament)
     end
+
     factory :stage_tournament do
       transient do
         stage_count { 1 }
@@ -19,5 +20,11 @@ FactoryBot.define do
         tournament.stages = create_list(:stage, evaluator.stage_count)
       end
     end
+
+    factory :group_stage_tournament do
+      after(:create) do |tournament, _evaluator|
+        tournament.stages = create_list(:group_stage, 1)
+      end
+    end
   end
 end
diff --git a/spec/interactors/add_group_stage_to_tournament_interactor_spec.rb b/spec/interactors/add_group_stage_to_tournament_interactor_spec.rb
new file mode 100644
index 0000000..b64c752
--- /dev/null
+++ b/spec/interactors/add_group_stage_to_tournament_interactor_spec.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+RSpec.describe AddGroupStageToTournament do
+  let(:empty_tournament_context) do
+    AddGroupStageToTournament.call(tournament: @empty_tournament, groups: @groups)
+  end
+
+  let(:group_stage_tournament_context) do
+    AddGroupStageToTournament.call(tournament: @group_stage_tournament, groups: @groups)
+  end
+
+  before do
+    @empty_tournament = create(:stage_tournament, stage_count: 0)
+    @group_stage_tournament = create(:group_stage_tournament)
+    @group_stage = create(:group_stage)
+    @groups = Hash[1 => create_list(:team, 4), 2 => create_list(:team, 4)].values
+  end
+
+  context 'GroupStageService mocked' do
+    before do
+      expect(class_double('GroupStageService').as_stubbed_const(transfer_nested_constants: true))
+        .to receive(:generate_group_stage).with(@groups)
+                                          .and_return(@group_stage)
+    end
+
+    context 'empty tournament' do
+      it 'succeeds' do
+        expect(empty_tournament_context).to be_a_success
+      end
+
+      it 'adds group stage to the tournament' do
+        test = empty_tournament_context.tournament.stages.first
+        expect(test).to eq(@group_stage)
+      end
+    end
+  end
+
+  context 'empty groups' do
+    before do
+      expect(class_double('GroupStageService').as_stubbed_const(transfer_nested_constants: true))
+        .to receive(:generate_group_stage).with(@groups)
+                                          .and_raise('Cannot generate group stage without groups')
+    end
+
+    it 'playoff generation fails' do
+      expect(empty_tournament_context).to be_a_failure
+    end
+  end
+
+  context 'unequal group sizes' do
+    before do
+      expect(class_double('GroupStageService').as_stubbed_const(transfer_nested_constants: true))
+        .to receive(:generate_group_stage).with(@groups)
+                                          .and_raise('Groups need to be equal size')
+    end
+
+    it 'playoff generation fails' do
+      expect(empty_tournament_context).to be_a_failure
+    end
+  end
+
+  context 'tournament where group stage is already generated' do
+    it 'does not add group stage' do
+      expect(group_stage_tournament_context).to be_a_failure
+    end
+  end
+end
diff --git a/spec/interactors/add_playoffs_to_tournament_interactor_spec.rb b/spec/interactors/add_playoffs_to_tournament_interactor_spec.rb
index 3bb385d..056dc2b 100644
--- a/spec/interactors/add_playoffs_to_tournament_interactor_spec.rb
+++ b/spec/interactors/add_playoffs_to_tournament_interactor_spec.rb
@@ -20,7 +20,7 @@ RSpec.describe AddPlayoffsToTournament do
     @stages = create_list(:stage, 5)
   end
 
-  context 'ez lyfe' do
+  context 'PlayoffStageService mocked' do
     before do
       expect(class_double('PlayoffStageService').as_stubbed_const(transfer_nested_constants: true))
         .to receive(:generate_playoff_stages_from_tournament)
diff --git a/spec/models/group_spec.rb b/spec/models/group_spec.rb
index 0f5784a..e8c8be2 100644
--- a/spec/models/group_spec.rb
+++ b/spec/models/group_spec.rb
@@ -12,4 +12,19 @@ RSpec.describe Group, type: :model do
   it 'has a valid factory' do
     expect(build(:group)).to be_valid
   end
+
+  describe '#teams' do
+    before do
+      @group = create(:group, match_count: 1) # this is getting stubbed anyways
+      @teams = create_list(:team, 4)
+      expect_any_instance_of(Match)
+        .to receive(:teams)
+        .and_return(@teams)
+    end
+
+    it 'returns all teams from the matches within the matches below' do
+      teams = @group.teams
+      expect(teams).to match_array(@teams)
+    end
+  end
 end
diff --git a/spec/models/match_spec.rb b/spec/models/match_spec.rb
index ad31ac6..01d34c5 100644
--- a/spec/models/match_spec.rb
+++ b/spec/models/match_spec.rb
@@ -43,7 +43,43 @@ RSpec.describe Match, type: :model do
     end
   end
 
+  context '#teams' do
+    before do
+      @playoff_match = create(:running_playoff_match)
+      @group_match = create(:running_group_match)
+      @teams = create_list(:team, 2)
+      @match_scores = create_list(:match_score, 2)
+      @match_scores.each_with_index { |match, i| match.team = @teams[i] }
+      @playoff_match.match_scores = @match_scores
+      @group_match.match_scores = @match_scores
+    end
+
+    context 'called on group match' do
+      let(:call_teams_on_group_match) do
+        @group_match.teams
+      end
+
+      it 'returns 2 team objects' do
+        teams = call_teams_on_group_match
+        expect(teams).to match_array(@teams)
+      end
+    end
+
+    context 'called on playoff match' do
+      let(:call_teams_on_playoff_match) do
+        @playoff_match.teams
+      end
+
+      it 'returns 2 team objects' do
+        teams = call_teams_on_playoff_match
+        expect(teams).to match_array(@teams)
+      end
+    end
+  end
+
   it 'has a valid factory' do
     expect(build(:match)).to be_valid
+    expect(build(:running_playoff_match)).to be_valid
+    expect(build(:group_match)).to be_valid
   end
 end
diff --git a/spec/models/stage_spec.rb b/spec/models/stage_spec.rb
index 4af3c30..a14fccd 100644
--- a/spec/models/stage_spec.rb
+++ b/spec/models/stage_spec.rb
@@ -11,5 +11,38 @@ RSpec.describe Stage, type: :model do
 
   it 'has a valid factory' do
     expect(build(:stage)).to be_valid
+    expect(build(:group_stage)).to be_valid
+  end
+
+  describe '#teams' do
+    context 'group stage' do
+      before do
+        @stage = create(:group_stage, group_count: 1) # this is getting stubbed anyways
+        @teams = create_list(:team, 4)
+        expect_any_instance_of(Group)
+          .to receive(:teams)
+          .and_return(@teams)
+      end
+
+      it 'returns all teams from the matches within the groups below' do
+        teams = @stage.teams
+        expect(teams).to match_array(@teams)
+      end
+    end
+
+    context 'playoff stage' do
+      before do
+        @stage = create(:playoff_stage, match_count: 1) # this is getting stubbed anyways
+        @teams = create_list(:team, 4)
+        expect_any_instance_of(Match)
+          .to receive(:teams)
+          .and_return(@teams)
+      end
+
+      it 'returns all teams from the matches within the matches below' do
+        teams = @stage.teams
+        expect(teams).to match_array(@teams)
+      end
+    end
   end
 end
diff --git a/spec/models/team_spec.rb b/spec/models/team_spec.rb
index ce229fa..d1e477b 100644
--- a/spec/models/team_spec.rb
+++ b/spec/models/team_spec.rb
@@ -15,5 +15,6 @@ RSpec.describe Team, type: :model do
 
   it 'has a valid factory' do
     expect(build(:team)).to be_valid
+    expect(build(:detached_team)).to be_valid
   end
 end
diff --git a/spec/models/tournament_spec.rb b/spec/models/tournament_spec.rb
index be6624a..c437df8 100644
--- a/spec/models/tournament_spec.rb
+++ b/spec/models/tournament_spec.rb
@@ -33,5 +33,7 @@ RSpec.describe Tournament, type: :model do
 
   it 'has valid factory' do
     expect(build(:tournament)).to be_valid
+    expect(build(:stage_tournament)).to be_valid
+    expect(build(:group_stage_tournament)).to be_valid
   end
 end
diff --git a/spec/services/group_stage_service_spec.rb b/spec/services/group_stage_service_spec.rb
new file mode 100644
index 0000000..f88f598
--- /dev/null
+++ b/spec/services/group_stage_service_spec.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+RSpec.describe GroupStageService do
+  before do
+    @stage = create(:stage)
+    @teams1 = create_list(:team, 4)
+    @teams2 = create_list(:team, 4)
+    @groups = Hash[1 => @teams1, 2 => @teams2].values
+  end
+  describe '#generate_group_stage method' do
+    it 'returns a stage object' do
+      group_stage = GroupStageService.generate_group_stage(@groups)
+      expect(group_stage).to be_a(Stage)
+    end
+
+    it 'returns a stage object with level -1' do
+      group_stage_level = GroupStageService.generate_group_stage(@groups).level
+      expect(group_stage_level).to be(-1)
+    end
+
+    it 'adds the provided groups to the stage' do
+      group_stage_teams = GroupStageService.generate_group_stage(@groups).teams
+      expect(group_stage_teams).to match_array(@groups.flatten)
+    end
+
+    it 'raises exception when given different sizes of groups' do
+      unequal_groups = @groups
+      unequal_groups.first.pop
+      expect { GroupStageService.generate_group_stage(unequal_groups) }
+        .to raise_exception 'Groups need to be equal size'
+    end
+
+    it 'raises exception when given no groups' do
+      expect { GroupStageService.generate_group_stage([]) }
+        .to raise_exception 'Cannot generate group stage without groups'
+    end
+  end
+
+  describe '#get_group_object_from' do
+    it 'returns a group' do
+      group = GroupStageService.get_group_object_from(@teams1)
+      expect(group).to be_a(Group)
+    end
+  end
+
+  describe '#generate_all_matches_between' do
+    it 'generates a list of not started matches' do
+      matches = GroupStageService.generate_all_matches_between(@teams2)
+      matches.each do |match|
+        expect(match).to be_a(Match)
+        match_state = match.state
+        expect(match_state).to eq('not_started')
+      end
+    end
+
+    it 'generates the right amount of matches' do
+      matches = GroupStageService.generate_all_matches_between(@teams2)
+      # (1..@teams2.size-1).sum -> 1. Team has to play against n-1 teams; second against n-2 ....
+      expect(matches.size).to be((1..@teams2.size - 1).sum)
+    end
+
+    it 'gives matches exclusive positions' do
+      matches = GroupStageService.generate_all_matches_between(@teams2)
+      match_positions = matches.map(&:position)
+      expect(match_positions.length).to eq(match_positions.uniq.length)
+    end
+
+    it 'doesn\'t match a team against itself' do
+      matches = GroupStageService.generate_all_matches_between(@teams1)
+      matches.each do |match|
+        expect(match.teams.first).to_not eq(match.teams.second)
+      end
+    end
+  end
+end