Complete Example: Write Tests Task (answer.md)

Use this complete, production-ready example to format your output when asked to write or verify RSpec tests.

Plan

1. Identify the Smallest Boundary: The task requires marking unpaid invoices overdue when their due date passes. Since this involves database query, state transition, and persistence logic, a PORO Service Spec (spec/services/invoices/mark_overdue_spec.rb) is the smallest strong boundary that fully isolates this domain behavior.
2. Draft the Spec First: Write the spec checking for state transition (change { invoice.reload.overdue? }.from(false).to(true)) and ignoring unrelated fields.
3. Execute TDD RED Gate: Run the spec command and capture the specific constant lookup failure (NameError: uninitialized constant Invoices::MarkOverdue).
4. Implement Minimal Code: Create the service class to satisfy the validations and pass the spec.
5. Execute TDD GREEN Gate: Re-run the spec to confirm passing status, and run the broader suite to ensure no regressions.
6. Apply Code Conventions & Linting: Audit the output against the 18-point checklist and ensure RuboCop passes.

Concrete Artifacts

1. Spec File

# spec/services/invoices/mark_overdue_spec.rb

# frozen_string_literal: true

require 'rails_helper'

RSpec.describe Invoices::MarkOverdue do
  describe '.call' do
    subject(:result) { described_class.call(invoice: invoice) }

    context 'when the invoice is unpaid and past its due date' do
      let(:invoice) { create(:invoice, due_date: 2.days.ago, paid_at: nil) }

      it 'marks the invoice overdue' do
        expect { result }.to change { invoice.reload.overdue? }.from(false).to(true)
      end
    end

    context 'when the invoice is already paid' do
      let(:invoice) { create(:invoice, due_date: 2.days.ago, paid_at: Time.current) }

      it 'does not mark the invoice overdue' do
        expect { result }.not_to change { invoice.reload.overdue? }
      end
    end
  end
end

2. Implementation File

# app/services/invoices/mark_overdue.rb

# frozen_string_literal: true

module Invoices
  class MarkOverdue
    def self.call(invoice:)
      return { success: false, error: 'Invoice already paid' } if invoice.paid_at.present?

      if invoice.due_date < Time.current
        invoice.update!(overdue: true)
        { success: true }
      else
        { success: false, error: 'Invoice not yet due' }
      end
    end
  end
end

TDD Execution Proof

1. Observed RED Output

Run Command:

bundle exec rspec spec/services/invoices/mark_overdue_spec.rb

Output:

An error occurred while loading ./spec/services/invoices/mark_overdue_spec.rb.
Failure/Error:
  RSpec.describe Invoices::MarkOverdue do

NameError:
  uninitialized constant Invoices::MarkOverdue
# ./spec/services/invoices/mark_overdue_spec.rb:5:in `<top (required)>'

Finished in 0.00005 seconds (files took 0.12 seconds to load)
0 examples, 0 failures, 1 error occurred outside of examples

2. Observed GREEN Output

Run Command:

bundle exec rspec spec/services/invoices/mark_overdue_spec.rb

Output:

..

Finished in 0.02415 seconds (files took 1.25 seconds to load)
2 examples, 0 failures

Verification & Quality Gates

Assumptions

1. ActiveRecord Persistence: Assumes Invoice has attributes due_date:datetime, paid_at:datetime, and overdue:boolean (default: false), matching the schema.
2. FactoryBot Setup: Assumes :invoice factory is registered and defaults to active, unpaid records.
3. Time-Cop Safety: Assumes the test suite uses travel_to for testing boundary conditions rather than setting static past dates in let without time freezing.
4. Environment: This test suite and implementation are verified against standard RSpec 3.x and Rails 7.x/8.x configurations.

Self-Audit Checklist

• No it/specify descriptions contain the word "and".
• Every let! is justified (none used here as lazy let is sufficient).
• Time-dependent records are created with dynamic attributes (2.days.ago).
• Factories use minimal persistent setup.
• All public APIs documented in English.