Help! Beginner Trying Test Driven Development.

I'm new to unit testing and Rails in general. I've decided to build my
projects in a TDD manner, but this has left me with some early
questions.
I have this test written out:

describe User do
  it "should add user to team" do
    team = Team.create(:name => "Tigers")
    akash = User.create(:name => "Akash")
    akash.teams << team
    akash.memberships.size.should == 1
    john = User.create(:name => "John")
    john.buddyup_with(akash)
    john.memberships.size.should == 1
    akash.buddys.should include(john)
  end
end

Ideally, users may join many teams, and teams may have many members. If
a user is paired up with another user through "buddyup", those users
will share all of the same teams.
I've started on the User model, but I'm lost at this point. Can
somebody help me out? Here's what I have so far:

class User < ActiveRecord::Base
  has_and_belongs_to_many :teams
  validates_presence_of :name
end

class Team < ActiveRecord::Base
  has_and_belongs_to_many :teams
  validates_presence_of :name
end

All I want to do is pass the test, further functionality will be added
later.

class Team < ActiveRecord::Base
  has_and_belongs_to_many :teams
  validates_presence_of :name
end

I suppose you mean :users instead of :teams