post_spec.rb

require 'rails_helper'

RSpec.describe Post, type: :model do
  context 'Associations' do
    it 'belongs_to user' do
      association = described_class.reflect_on_association(:user).macro
      expect(association).to eq :belongs_to
    end

    it 'belongs_to category' do
      association = described_class.reflect_on_association(:category).macro
      expect(association).to eq :belongs_to
    end
  end
end

The duplicate on the user association testing (line 11) is corrected here but the duplicate is still here on your repository: https://github.com/domagude/collabfield/blob/master/spec/models/post_spec.rb