x.rb

class Contact
  def opted_out?
    project_contacts.where(opted_out: true).count == project_contacts.count
  end
end

describe "#opted_out?" do
  let(:project_contacts) { double("project_contacts", count: 1) }

  before do
    expect(subject).to receive(:project_contacts).twice { project_contacts }
  end

  describe "when all projects are opted out" do
    it "returns true" do
      expect(project_contacts).to receive(:where).with(opted_out: true) { double(count: 1) }
      expect(subject.opted_out?).to be_true
    end
  end

  describe "when no projects are opted out" do
    it "returns false" do
      expect(project_contacts).to receive(:where).with(opted_out: true) { double(count: 0) }
      expect(subject.opted_out?).to be_false
    end
  end
end