login ok

app/assets/javascripts/sessions.js.coffee

+# Place all the behaviors and hooks related to the matching controller here.
+# All this logic will automatically be available in application.js.
+# You can use CoffeeScript in this file: http://coffeescript.org/

app/assets/stylesheets/sessions.css.scss

+// Place all the styles related to the Sessions controller here.
+// They will automatically be included in application.css.
+// You can use Sass (SCSS) here: http://sass-lang.com/

app/controllers/sessions_controller.rb

+class SessionsController < ApplicationController
+  def new
+  end
+
+	def create
+		user = User.find_by(email: params[:session][:email].downcase)
+		if user && user.authenticate(params[:session][:password])
+			# Log the user in and redirect to the user's show page.
+			log_in user
+			redirect_to user
+		else
+			flash.now[:danger] = "Invalid email/password combination"
+			render 'new'
+		end
+	end
+
+	def destroy
+	end
+end

app/helpers/sessions_helper.rb

+module SessionsHelper
+	def log_in(user)
+		session[:user_id] = user.id
+	end
+
+	def current_user
+		@current_user ||= User.find_by(id: session[:user_id])
+	end
+
+	def logged_in?
+		!current_user.nil?
+	end
+end

app/views/sessions/new.html.erb

+<% provide(:title, "Log in") %>
+<h1> Log in</h1>
+
+<div class="row">
+	<div class="col-md-6 col-md-offset-3">
+		<%= form_for(:session, url: login_path) do |f| %>
+			<%= f.label :email %>
+			<%= f.text_field :email, class: 'form-control' %>
+			<%= f.label :password %>
+			<%= f.password_field :password, class: 'form-control' %>
+			<%= f.submit "Log in", class: "btn btn-primary" %>
+		<% end %>
+		<p>New user? <%= link_to "Sign up now!", signup_path %></p>
+	</div>
+</div>

test/controllers/sessions_controller_test.rb

+require 'test_helper'
+
+class SessionsControllerTest < ActionController::TestCase
+  test "should get new" do
+    get :new
+    assert_response :success
+  end
+
+end

test/integration/users_login_test.rb

+require 'test_helper'
+
+class UsersLoginTest < ActionDispatch::IntegrationTest
+	test "login with invalid information" do
+		get login_path
+		assert_template 'sessions/new'
+		post login_path, session: {email: "", password: ""}
+		assert_template 'sessions/new'
+		assert_not flash.empty?
+		get root_path
+		assert flash.empty?
+	end
+end