diff --git a/app/models/user.rb b/app/models/user.rb
index b60721274..8228f67e0 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class User < ApplicationRecord
   include SearchableModel
   include SettingsModel
diff --git a/app/models/user_identity.rb b/app/models/user_identity.rb
index 2d1f46a23..01775e1bd 100644
--- a/app/models/user_identity.rb
+++ b/app/models/user_identity.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UserIdentity < ActiveRecord::Base
   belongs_to :user
   validates :provider, presence: true, uniqueness: { scope: :user_id }
diff --git a/app/models/user_my_module.rb b/app/models/user_my_module.rb
index 5b3edabb4..3ba35879d 100644
--- a/app/models/user_my_module.rb
+++ b/app/models/user_my_module.rb
@@ -1,13 +1,10 @@
+# frozen_string_literal: true
+
 class UserMyModule < ApplicationRecord
   validates :user, presence: true, uniqueness: { scope: :my_module }
   validates :my_module, presence: true
 
-  belongs_to :user, inverse_of: :user_my_modules, touch: true, optional: true
-  belongs_to :assigned_by,
-             foreign_key: 'assigned_by_id',
-             class_name: 'User',
-             optional: true
-  belongs_to :my_module, inverse_of: :user_my_modules,
-                         touch: true,
-                         optional: true
+  belongs_to :user, inverse_of: :user_my_modules, touch: true
+  belongs_to :assigned_by, foreign_key: 'assigned_by_id', class_name: 'User', optional: true
+  belongs_to :my_module, inverse_of: :user_my_modules, touch: true
 end
diff --git a/app/models/user_notification.rb b/app/models/user_notification.rb
index d034a563c..83226548f 100644
--- a/app/models/user_notification.rb
+++ b/app/models/user_notification.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UserNotification < ApplicationRecord
   include NotificationsHelper
 
diff --git a/app/models/user_project.rb b/app/models/user_project.rb
index cbaeb4ac0..b63ede753 100644
--- a/app/models/user_project.rb
+++ b/app/models/user_project.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UserProject < ApplicationRecord
   enum role: { owner: 0, normal_user: 1, technician: 2, viewer: 3 }
 
@@ -5,12 +7,9 @@ class UserProject < ApplicationRecord
   validates :user, presence: true, uniqueness: { scope: :project }
   validates :project, presence: true
 
-  belongs_to :user, inverse_of: :user_projects, touch: true, optional: true
-  belongs_to :assigned_by,
-             foreign_key: 'assigned_by_id',
-             class_name: 'User',
-             optional: true
-  belongs_to :project, inverse_of: :user_projects, touch: true, optional: true
+  belongs_to :user, inverse_of: :user_projects, touch: true
+  belongs_to :assigned_by, foreign_key: 'assigned_by_id', class_name: 'User', optional: true
+  belongs_to :project, inverse_of: :user_projects, touch: true
 
   before_destroy :destroy_associations
   validates_uniqueness_of :user_id, scope: :project_id
diff --git a/app/models/user_team.rb b/app/models/user_team.rb
index 87cc5fd25..45f5f7f70 100644
--- a/app/models/user_team.rb
+++ b/app/models/user_team.rb
@@ -1,16 +1,13 @@
+# frozen_string_literal: true
+
 class UserTeam < ApplicationRecord
   enum role: { guest: 0, normal_user: 1, admin: 2 }
 
-  validates :role, presence: true
-  validates :user, presence: true
-  validates :team, presence: true
+  validates :role, :user, :team, presence: true
 
-  belongs_to :user, inverse_of: :user_teams, touch: true, optional: true
-  belongs_to :assigned_by,
-             foreign_key: 'assigned_by_id',
-             class_name: 'User',
-             optional: true
-  belongs_to :team, inverse_of: :user_teams, optional: true
+  belongs_to :user, inverse_of: :user_teams, touch: true
+  belongs_to :assigned_by, foreign_key: 'assigned_by_id', class_name: 'User', optional: true
+  belongs_to :team, inverse_of: :user_teams
 
   before_destroy :destroy_associations
   after_create :create_samples_table_state
diff --git a/spec/factories/user_identities.rb b/spec/factories/user_identities.rb
index c9035a241..c33e17570 100644
--- a/spec/factories/user_identities.rb
+++ b/spec/factories/user_identities.rb
@@ -1,5 +1,8 @@
+# frozen_string_literal: true
+
 FactoryBot.define do
   factory :user_identity do
+    user
     uid Faker::Crypto.unique.sha1
     provider Faker::App.unique.name
   end
diff --git a/spec/factories/user_notification.rb b/spec/factories/user_notifications.rb
similarity index 72%
rename from spec/factories/user_notification.rb
rename to spec/factories/user_notifications.rb
index 3eee80e4a..579e8cdf8 100644
--- a/spec/factories/user_notification.rb
+++ b/spec/factories/user_notifications.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 FactoryBot.define do
   factory :user_notification do
     checked false
diff --git a/spec/factories/user_teams.rb b/spec/factories/user_teams.rb
index ee52a9af9..c13c75db5 100644
--- a/spec/factories/user_teams.rb
+++ b/spec/factories/user_teams.rb
@@ -2,6 +2,8 @@
 
 FactoryBot.define do
   factory :user_team do
+    user
+    team
     trait :admin do
       role 'admin'
     end
diff --git a/spec/factories/view_states.rb b/spec/factories/view_states.rb
index eb819d592..d898bef59 100644
--- a/spec/factories/view_states.rb
+++ b/spec/factories/view_states.rb
@@ -3,7 +3,7 @@
 FactoryBot.define do
   factory :view_state do
     state {}
-    user { User.first || create(:user) }
-    viewable { Team.first || create(:team) }
+    user
+    viewable { create :team }
   end
 end
diff --git a/spec/models/user_identity_spec.rb b/spec/models/user_identity_spec.rb
new file mode 100644
index 000000000..23179a1ba
--- /dev/null
+++ b/spec/models/user_identity_spec.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe UserIdentity, type: :model do
+  let(:user_identity) { build :user_identity }
+
+  it 'is valid' do
+    expect(user_identity).to be_valid
+  end
+
+  it 'should be of class UserIdentity' do
+    expect(subject.class).to eq UserIdentity
+  end
+
+  describe 'Relations' do
+    it { is_expected.to belong_to :user }
+  end
+
+  describe 'Validations' do
+    describe '#uid' do
+      it { is_expected.to validate_presence_of :uid }
+      it { expect(user_identity).to validate_uniqueness_of(:uid).scoped_to(:provider) }
+    end
+
+    describe '#provider' do
+      it { is_expected.to validate_presence_of :provider }
+      it { expect(user_identity).to validate_uniqueness_of(:provider).scoped_to(:user_id) }
+    end
+  end
+end
diff --git a/spec/models/user_my_module_spec.rb b/spec/models/user_my_module_spec.rb
index 5ba89fdef..466a74b92 100644
--- a/spec/models/user_my_module_spec.rb
+++ b/spec/models/user_my_module_spec.rb
@@ -1,6 +1,14 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserMyModule, type: :model do
+  let(:user_my_module) { build :user_my_module }
+
+  it 'is valid' do
+    expect(user_my_module).to be_valid
+  end
+
   it 'should be of class UserMyModule' do
     expect(subject.class).to eq UserMyModule
   end
@@ -19,7 +27,7 @@ describe UserMyModule, type: :model do
     it { should belong_to(:assigned_by).class_name('User') }
   end
 
-  describe 'Should be a valid object' do
+  describe 'Validations' do
     it { should validate_presence_of :user }
     it { should validate_presence_of :my_module }
   end
diff --git a/spec/models/user_notification_spec.rb b/spec/models/user_notification_spec.rb
index a7ba560f2..c59645ee3 100644
--- a/spec/models/user_notification_spec.rb
+++ b/spec/models/user_notification_spec.rb
@@ -1,7 +1,14 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserNotification, type: :model do
   let(:user) { create :user }
+  let(:user_notification) { build :user_notification }
+
+  it 'is valid' do
+    expect(user_notification).to be_valid
+  end
 
   it 'should be of class UserNotification' do
     expect(subject.class).to eq UserNotification
diff --git a/spec/models/user_project_spec.rb b/spec/models/user_project_spec.rb
index 18883e775..3c8a29c1f 100644
--- a/spec/models/user_project_spec.rb
+++ b/spec/models/user_project_spec.rb
@@ -1,6 +1,19 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserProject, type: :model do
+  let(:user_project_without_role) { build :user_project }
+  let(:user_project) { build :user_project, :owner }
+
+  it 'is invalid without role' do
+    expect(user_project_without_role).not_to be_valid
+  end
+
+  it 'is valid with role' do
+    expect(user_project).to be_valid
+  end
+
   it 'should be of class UserProject' do
     expect(subject.class).to eq UserProject
   end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 20c46deab..7db2650c0 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -3,6 +3,11 @@
 require 'rails_helper'
 
 describe User, type: :model do
+  let(:user) { build :user }
+
+  it 'is valid' do
+    expect(user).to be_valid
+  end
   it 'should be of class User' do
     expect(subject.class).to eq User
   end
@@ -120,7 +125,7 @@ describe User, type: :model do
     end
   end
 
-  describe 'Should be a valid object' do
+  describe 'Validations' do
     it { should validate_presence_of :full_name }
     it { should validate_presence_of :initials  }
     it { should validate_presence_of :email }
diff --git a/spec/models/user_team_spec.rb b/spec/models/user_team_spec.rb
index 8ca01063f..1f98c469d 100644
--- a/spec/models/user_team_spec.rb
+++ b/spec/models/user_team_spec.rb
@@ -1,6 +1,14 @@
+# frozen_string_literal: true
+
 require 'rails_helper'
 
 describe UserTeam, type: :model do
+  let(:user_team) { build :user_team }
+
+  it 'is valid' do
+    expect(user_team).to be_valid
+  end
+
   it 'should be of class UserTeam' do
     expect(subject.class).to eq UserTeam
   end
@@ -20,7 +28,7 @@ describe UserTeam, type: :model do
     it { should belong_to(:assigned_by).class_name('User') }
   end
 
-  describe 'Should be a valid object' do
+  describe 'Validations' do
     it { should validate_presence_of :role }
     it { should validate_presence_of :user }
     it { should validate_presence_of :team }
diff --git a/spec/models/view_state_spec.rb b/spec/models/view_state_spec.rb
index 532ed1db3..3ededbfd5 100644
--- a/spec/models/view_state_spec.rb
+++ b/spec/models/view_state_spec.rb
@@ -3,6 +3,12 @@
 require 'rails_helper'
 
 RSpec.describe ViewState, type: :model do
+  let(:view_state) { build :view_state }
+
+  it 'is valid' do
+    expect(view_state).to be_valid
+  end
+
   it 'should be of class ViewState' do
     expect(subject.class).to eq ViewState
   end