diff --git a/app/models/user.rb b/app/models/user.rb
index cee87c8..e67bdfa 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1,7 +1,7 @@
 class User < ApplicationRecord
   # -- Validations
   validates :email, presence: true, uniqueness: true
-  validates :password, presence: true, length: {minimum: 8}
+  validates :password, presence: true, length: { minimum: 8 }
   validates :role, presence: true
 
   # -- Associations
diff --git a/spec/factories/posts.rb b/spec/factories/posts.rb
index 402d675..c335d6b 100644
--- a/spec/factories/posts.rb
+++ b/spec/factories/posts.rb
@@ -1,3 +1,7 @@
 FactoryBot.define do
-  # Implementar factory
+  factory :post do
+    association :user
+    title { Faker::Lorem.unique.word }
+    body  { Faker::Lorem.sentence(30) }
+  end
 end
diff --git a/spec/factories/users.rb b/spec/factories/users.rb
index 72d97d1..f4e0b16 100644
--- a/spec/factories/users.rb
+++ b/spec/factories/users.rb
@@ -1,7 +1,7 @@
 FactoryBot.define do
   factory :user do
     auth_token { SecureRandom.hex }
-    email { Faker::Internet.email }
+    email { Faker::Internet.unique.email }
     password { SecureRandom.uuid }
 
     # Definición de atributos transitorios o transients
diff --git a/spec/models/post_spec.rb b/spec/models/post_spec.rb
index 2162433..f7dbc77 100644
--- a/spec/models/post_spec.rb
+++ b/spec/models/post_spec.rb
@@ -3,4 +3,26 @@
 RSpec.describe Post, type: :model do
   # En base al modelo de test propuesto para el modelo User,
   # implementar los tests para el modelo Post.
+  describe 'Factory' do
+    it 'has a valid factory' do
+      expect(build(:post)).to be_valid
+    end
+  end
+
+  describe 'Associations' do
+    it { should belong_to(:user) }
+    # https://github.com/thoughtbot/shoulda-matchers#activerecord-matchers
+  end
+
+  describe 'Presence validations' do
+    it { should validate_presence_of(:title) }
+    it { should validate_presence_of(:body) }
+    # https://github.com/thoughtbot/shoulda-matchers#activemodel-matchers
+  end
+
+  describe 'Uniqueness validations' do
+    subject { create(:post) }
+    it { should validate_uniqueness_of(:title) }
+    # https://github.com/thoughtbot/shoulda-matchers#activemodel-matchers
+  end
 end
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 4db8f67..a040a81 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -3,37 +3,51 @@
 RSpec.describe User, type: :model do
   describe 'Factory' do
     it 'has a valid factory' do
-      # Testear que el factory definido es válido.
+      expect(build(:user)).to be_valid
     end
   end
 
   describe 'Associations' do
-    # Testear asociaciones (shoulda-matchers).
+    it { should have_many(:posts) }
     # https://github.com/thoughtbot/shoulda-matchers#activerecord-matchers
   end
 
   describe 'Presence validations' do
-    # Testear validaciones de presencia (shoulda-matchers).
+    it { should validate_presence_of(:email) }
+    it { should validate_presence_of(:password) }
+    it { should validate_presence_of(:role) }
     # https://github.com/thoughtbot/shoulda-matchers#activemodel-matchers
   end
 
   describe 'Uniqueness validations' do
-    # Testear validaciones de unicidad (shoulda-matchers).
+    subject { create(:user) }
+    it { should validate_uniqueness_of(:email) }
     # https://github.com/thoughtbot/shoulda-matchers#activemodel-matchers
   end
 
   describe 'Length validations' do
-    # Testear validaciones de longitud (shoulda-matchers).
+    it { should validate_length_of(:password).is_at_least(8) }
     # https://github.com/thoughtbot/shoulda-matchers#activemodel-matchers
   end
 
   describe 'Enumeratives' do
-    # Testear definición de enumerativos (shoulda-matchers).
+    it { should define_enum_for(:role) }
   end
 
-  # Testear métodos de instancia y de clase como para el caso de cualquier
-  # otra clase Ruby (similar a testear ApiLoginManager).
   describe '#valid_password?' do
+    subject { create(:user) }
+    context 'when given value is different from password' do
+      it 'returns false' do
+        expect(subject.valid_password?(SecureRandom.uuid)).to be_falsey
+      end
+    end
+
+    context 'when given value is equal to password' do
+      it 'returns true' do
+        expect(subject.valid_password?(subject.password)).to be
+      end
+    end
+
     # Testear funcionamiento de método. Podemos definir dos contexts:
     #  - 'when given value is different from password'
     #  - 'when given value is equal to password'
diff --git a/spec/services/api_login_manager_spec.rb b/spec/services/api_login_manager_spec.rb
index 5ea0316..05447a1 100644
--- a/spec/services/api_login_manager_spec.rb
+++ b/spec/services/api_login_manager_spec.rb
@@ -11,11 +11,12 @@
   # en let!(:user) { ... }, usar esta variable.
   let!(:password) { SecureRandom.hex }
 
-  let!(:user) {  } # -- crear usuario con FactoryBot -- #
+  let!(:user) { create(:user, password: password) } # -- crear usuario con FactoryBot -- #
 
   describe '#call' do
     context 'when user provided data is valid' do
       before do
+        allow(ExternalValidator).to receive(:call).and_return(true)
         # Realizar un stub del ExternalValidator para que se ejecuta realmente
       end
 
@@ -24,60 +25,87 @@
       end
 
       it "update user's auth_token" do
-        skip 'Una vez que definan a user, este test va a fallar. ¿Por qué?'
-        expect { subject }.to change { user.auth_token }
+        expect { subject }.to change { user.reload.auth_token }
       end
 
       it 'returns the auth_token' do
-        skip 'Implementar'
+        expect(subject).to eq(user.reload.auth_token)
       end
     end
 
     context 'when no email is provided' do
-      subject {  } # implementar
+      subject { described_class.new(password: password) }
 
       it 'returns false' do
-        skip 'Implementar'
+        expect(subject.call).to be_falsey
       end
 
       it 'returns EMPTY_EMAIL error with a reader' do
-        skip 'Implementar'
+        subject.call
+        expect(subject.error).to be(ApiLoginManager::EMPTY_EMAIL)
       end
     end
 
     context 'when no password is provided' do
-      subject {  } # implementar
+      subject { described_class.new(email: user.email) }
 
       it 'returns false' do
-        skip 'Implementar'
+        expect(subject.call).to be_falsey
       end
 
       it 'returns EMPTY_PASSWORD error with a reader' do
-        skip 'Implementar'
+        subject.call
+        expect(subject.error).to be(ApiLoginManager::EMPTY_PASSWORD)
       end
     end
 
     context 'when the email is incorrect' do
-      subject {  } # implementar
+      subject do
+        described_class.new(
+          email: Faker::Internet.unique.email,
+          password: user.password
+        )
+      end
 
       it 'returns false' do
-        skip 'Implementar'
+        expect(subject.call).to be_falsey
       end
 
       it 'returns USER_NOT_FOUND error with a reader' do
-        skip 'Implementar'
+        subject.call
+        expect(subject.error).to be(ApiLoginManager::USER_NOT_FOUND)
       end
     end
 
     context 'when the password is incorrect' do
-      subject {  } # implementar
+      subject do
+        described_class.new(email: user.email, password: SecureRandom.uuid)
+      end
 
       it 'returns false' do
-        skip 'Implementar'
+        expect(subject.call).to be_falsey
       end
 
       it 'returns WRONG_PASSWORD error with a reader' do
-        skip 'Implementar'
+        subject.call
+        expect(subject.error).to be(ApiLoginManager::WRONG_PASSWORD)
+      end
+    end
+
+    context 'when ExternalValidator fails' do
+      before do
+        allow(ExternalValidator).to receive(:call).and_return(false)
+      end
+
+      subject { described_class.new(email: user.email, password: user.password) }
+
+      it 'returns false' do
+        expect(subject.call).to be_falsey
+      end
+
+      it 'returns EXTERNAL_VALIDATOR error with a reader' do
+        subject.call
+        expect(subject.error).to be(ApiLoginManager::EXTERNAL_VALIDATOR)
       end
     end