## users_controller_test.rb

  def test_should_login_user_valid
    params = {:user => {:username => users(:valid).username, :password => users(:valid).password}}
    post :login, params
    assert_redirected_to dashboard_url
  end

## users_controller.rb

def login
    if request.post?

      @user = User.authenticate(params[:user][:username], MD5.new(params[:user][:password]).hexdigest)
      unless @user.nil?
          session[:user] = @user
          flash[:notice] = "Successfully logged in. Welcome #{session[:user].username}"
          redirect_to dashboard_url
      else
          flash.now[:warning] = "You could not be logged in with the provided credentials."
      end

    end

  end

## users/_login.html.erb

<% form_for(:user) do |u| %>

<%= u.label :username %><%= u.text_field :username %><br />
<%= u.label :password %><%= u.password_field :password %><br />
<br />
<%= u.submit "Login", :disable_with => "Logging in..." %>
<br />
<% end %>

## models/user.rb

def self.authenticate(username, password)
    find(:first, :conditions => ["username = ? AND password = ?", username, password])
  end

## fixtures/users.yml

valid:
    username: ValidUser1
    password: <%= MD5.new('test').hexdigest %>
    email: validEmail@email.com
    created_at: <%= 3.months.ago.to_s(:db) %>
    updated_at: <%= 2.weeks.ago.to_s(:db) %>