Practical (or too dirty?) way of testing something

spec__models__concerns__durable_record_spec.rb

require 'spec_helper'

shared_examples_for 'durable_record' do
  let(:duration) { nil }
  let(:end_date) { nil }
  let(:start_date) { nil }
  let(:instance) { described_class.new }
  let(:attributes) do
    { duration: duration, end_date: end_date, start_date: start_date }
  end

  subject do
    pure_assign(instance, attributes)
    instance.send(method, value)
    instance.attributes.values_at(*%w[duration end_date start_date])
  end

  describe '#duration=' do
    let(:method) { :duration= }

    context 'when start_date is set and duration provided is not nil' do
      let(:start_date) { Date.civil(2018, 11, 19) }
      let(:value) { 2 }
      let(:expected_end_date) { Date.civil(2018, 11, 21) }

      it { is_expected.to eq([value, expected_end_date, start_date]) }
    end

    context 'when end_date is set and duration provided is not nil' do
      let(:end_date) { Date.civil(2018, 11, 19) }
      let(:value) { 4 }
      let(:expected_start_date) { Date.civil(2018, 11, 15) }

      it { is_expected.to eq([value, end_date, expected_start_date]) }
    end

    context 'when start_date and end_date are set and duration provided is nil' do
      let(:start_date) { Date.civil(2018, 11, 19) }
      let(:end_date) { Date.civil(2018, 11, 22) }
      let(:value) { nil }
      let(:expected_duration) { 3 }

      it { is_expected.to eq([expected_duration, end_date, start_date]) }
    end

    context 'when all three attributes are not set and duration is provided' do
      let(:value) { 3 }

      it { is_expected.to eq([value, nil, nil]) }
    end
  end

  describe '#end_date=' do
    let(:method) { :end_date= }

    context 'when start_date is set and end_date provided is not nil' do
      let(:start_date) { Date.civil(2018, 11, 14) }
      let(:value) { Date.civil(2018, 11, 21) }
      let(:expected_duration) { 7 }

      it { is_expected.to eq([expected_duration, value, start_date]) }
    end

    context 'when duration is set and end_date provided is not nil' do
      let(:duration) { 2 }
      let(:value) { Date.civil(2018, 11, 20) }
      let(:expected_start_date) { Date.civil(2018, 11, 18) }

      it { is_expected.to eq([duration, value, expected_start_date]) }
    end

    context 'when duration and start_date are set and end_date provided is nil' do
      let(:duration) { 3 }
      let(:start_date) { Date.civil(2018, 11, 12) }
      let(:value) { nil }
      let(:expected_end_date) { Date.civil(2018, 11, 15) }

      it { is_expected.to eq([duration, expected_end_date, start_date]) }
    end

    context 'when all three attributes are not set and end_date is provided' do
      let(:value) { Date.civil(2018, 11, 17) }

      it { is_expected.to eq([nil, value, nil]) }
    end
  end

  describe '#start_date=' do
    let(:method) { :start_date= }

    context 'when duration is set and start_date provided is not nil' do
      let(:duration) { 10 }
      let(:value) { Date.civil(2018, 11, 15) }
      let(:expected_end_date) { Date.civil(2018, 11, 25) }

      it { is_expected.to eq([duration, expected_end_date, value]) }
    end

    context 'when end_date is set and start_date provided is not nil' do
      let(:end_date) { Date.civil(2018, 11, 20) }
      let(:value) { Date.civil(2018, 11, 15) }
      let(:expected_duration) { 5 }

      it { is_expected.to eq([expected_duration, end_date, value]) }
    end

    context 'when duration and end_date are set and start_date provided is nil' do
      let(:duration) { 3 }
      let(:end_date) { Date.civil(2018, 11, 12) }
      let(:value) { nil }
      let(:expected_start_date) { Date.civil(2018, 11, 9) }

      it { is_expected.to eq([duration, end_date, expected_start_date]) }
    end

    context 'when all three attributes are not set and end_date is provided' do
      let(:value) { Date.civil(2018, 11, 19) }

      it { is_expected.to eq([nil, nil, value]) }
    end
  end
end