conversation_spec.rb

...
context 'Methods' do
  it 'gets an opposed user of the conversation' do
    user1 = create(:user)
    user2 = create(:user)
    conversation = create(:private_conversation,
                           recipient_id: user1.id,
                           sender_id: user2.id)
    opposed_user = conversation.opposed_user(user1)
    expect(opposed_user).to eq user2
  end
end
...