You start with this:

def update
	test do
	  user_in_db = @user.reload
	  user_in_db.password.should == params[:new_password]
  end
end

Then add some code:

def update
  @user = User.find(params[:id])
  @user.password = params[:new_password]
	test do
	  user_in_db = @user.reload
	  user_in_db.password.should == params[:new_password]
  end
end

Oops, it will fail next time it will be used, so we fix it:

def update
  @user = User.find(params[:id])
  @user.password = params[:new_password]
  @user.save
	test do
	  user_in_db = @user.reload
	  user_in_db.password.should == params[:new_password]
  end
end

Now, lets imagine that somebody created a trigger on `users` updates that does something wrong with the password :) The above test will fail as soon as anybody will try to change the password!