start writing tests

app/controllers/sessions_controller.rb

@@ -6,17 +6,35 @@ class SessionsController < ApplicationController
 
   # GET /logout
   def destroy
-    logout
+    logout if current_user
+  end
+
+  # POST /login
+  def create
+    user = User.find_by(email: session_params[:email])
+    if user && user.authenticate(session_params[:password])
+      login(user)
+    else
+      # Login unsuccessful, display error message.
+      
+      render :new
+    end
   end
 
   # GET/POST /auth/:provider/callback
-  def create
+  def omniauth_session
     user = User.from_omniauth(request.env['omniauth.auth'])
     login(user)
   end
 
   # POST /auth/failure
   def fail
+    redirect_to root_path
+  end
 
+  private
+
+  def session_params
+    params.require(:session).permit(:email, :password)
   end
 end