diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index 294c008..e1e1047 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -6,7 +6,8 @@ def new
 
   def create
     user = User.where("email = ?", params[:email].downcase).first
-    if AuthenticateUser.call(user, params)
+    authentication = AuthenticateUser.new(user, params).call
+    if authentication.success?
       set_cookie(user, params)
       redirect_to(sign_in_destination)
     else
diff --git a/app/services/authenticate_user.rb b/app/services/authenticate_user.rb
index 049c7bd..c13e0e6 100644
--- a/app/services/authenticate_user.rb
+++ b/app/services/authenticate_user.rb
@@ -1,11 +1,22 @@
 class AuthenticateUser
 
-  def self.call(user, params)
-    if user && user.authenticate(params[:password])
-      true
+  def initialize(user, params)
+    @user = user
+    @params = params
+    @result = false
+  end
+
+  def call
+    if @user && @user.authenticate(@params[:password])
+      @result = true
     else
-      false
+      @result = false
     end
+    self
+  end
+
+  def success?
+    @result
   end
 
 end
diff --git a/spec/services/authenticate_user_spec.rb b/spec/services/authenticate_user_spec.rb
new file mode 100644
index 0000000..faf3071
--- /dev/null
+++ b/spec/services/authenticate_user_spec.rb
@@ -0,0 +1,32 @@
+require 'rails_helper'
+
+RSpec.describe AuthenticateUser do
+
+  subject { AuthenticateUser.new(user, params).call }
+
+  describe 'for unknown user' do
+    let(:user) { nil }
+    let(:params) { {} }
+    it 'is unsuccessful' do
+      expect(subject.success?).to be false
+    end
+  end
+
+  describe 'for known user' do
+    let(:user) { Fabricate.build(:user) }
+
+    context 'with correct password' do
+      let(:params) { { password: user.password } }
+      it 'is successful' do
+        expect(subject.success?).to be true
+      end
+    end
+
+    context 'with incorrect password' do
+      let(:params) { { password: 'wrongpassword' } }
+      it 'is unsuccessful' do
+        expect(subject.success?).to be false
+      end
+    end
+  end
+end