Refactor and improve invoices

- `runner 'Invoice.cancel_overdue_invoices'` in `schedule.rb` is
changed to `rake 'invoices:cancel_overdue'`.
- `invoices.payment_term` database column is removed and its value is
hardcoded in UI.
- `invoices.paid_at` is removed as unused
- `invoices.due_date` column's type is now `date`.
- `Invoice#invoice_items` renamed to `Invoice#items` and `Invoice`
interface to get a list of items is unified.
- Default date format in UI.
- Default translations are used.
- Tests improved.
- Specs converted to tests and removed along with factories.
- Database structure improved.

test/models/invoice_test.rb

@@ -2,11 +2,40 @@ require 'test_helper'
 
 class InvoiceTest < ActiveSupport::TestCase
   setup do
-    @invoice = invoices(:valid)
+    @invoice = invoices(:one)
   end
 
-  def test_valid
-    assert @invoice.valid?
+  def test_fixture_is_valid
+    assert @invoice.valid?, proc { @invoice.errors.full_messages }
+  end
+
+  def test_overdue_scope_returns_unpaid_uncancelled_invoices_with_past_due_date
+    travel_to Time.zone.parse('2010-07-05')
+    @invoice.update!(account_activity: nil, cancelled_at: nil, due_date: '2010-07-04')
+
+    assert Invoice.overdue.include?(@invoice), 'Should return overdue invoice'
+  end
+
+  def test_overdue_scope_does_not_return_paid_invoices
+    assert @invoice.paid?
+    assert_not Invoice.overdue.include?(@invoice), 'Should not return paid invoice'
+  end
+
+  def test_overdue_scope_does_not_return_cancelled_invoices
+    @invoice.update!(cancelled_at: '2010-07-05')
+    assert_not Invoice.overdue.include?(@invoice), 'Should not return cancelled invoice'
+  end
+
+  def test_overdue_scope_does_not_return_invoices_with_due_due_of_today_or_in_the_future
+    travel_to Time.zone.parse('2010-07-05')
+    @invoice.update!(due_date: '2010-07-05')
+
+    assert_not Invoice.overdue.include?(@invoice), 'Should not return non-overdue invoice'
+  end
+
+  def test_invalid_without_issue_date
+    @invoice.issue_date = nil
+    assert @invoice.invalid?
   end
 
   def test_optional_vat_rate
@@ -30,7 +59,7 @@ class InvoiceTest < ActiveSupport::TestCase
 
   def test_serializes_and_deserializes_vat_rate
     invoice = @invoice.dup
-    invoice.invoice_items = @invoice.invoice_items
+    invoice.items = @invoice.items
     invoice.vat_rate = BigDecimal('25.5')
     invoice.save!
     invoice.reload
@@ -42,7 +71,7 @@ class InvoiceTest < ActiveSupport::TestCase
     invoice = @invoice.dup
     invoice.vat_rate = nil
     invoice.buyer = registrar
-    invoice.invoice_items = @invoice.invoice_items
+    invoice.items = @invoice.items
 
     registrar.stub(:effective_vat_rate, BigDecimal(55)) do
       invoice.save!
@@ -59,7 +88,9 @@ class InvoiceTest < ActiveSupport::TestCase
   end
 
   def test_calculates_vat_amount
-    assert_equal BigDecimal('1.5'), @invoice.vat_amount
+    invoice_item = InvoiceItem.new(price: 25, quantity: 2)
+    invoice = Invoice.new(vat_rate: 10, items: [invoice_item, invoice_item.dup])
+    assert_equal 10, invoice.vat_amount
   end
 
   def test_vat_amount_is_zero_when_vat_rate_is_blank
@@ -69,7 +100,7 @@ class InvoiceTest < ActiveSupport::TestCase
 
   def test_calculates_subtotal
     line_item = InvoiceItem.new
-    invoice = Invoice.new(invoice_items: [line_item, line_item])
+    invoice = Invoice.new(items: [line_item, line_item])
 
     line_item.stub(:item_sum_without_vat, BigDecimal('2.5')) do
       assert_equal BigDecimal(5), invoice.subtotal
@@ -84,7 +115,7 @@ class InvoiceTest < ActiveSupport::TestCase
     line_item = InvoiceItem.new
     invoice = Invoice.new
     invoice.vat_rate = 10
-    invoice.invoice_items = [line_item, line_item]
+    invoice.items = [line_item, line_item]
 
     line_item.stub(:item_sum_without_vat, BigDecimal('2.5')) do
       assert_equal BigDecimal('5.50'), invoice.total
@@ -102,8 +133,25 @@ class InvoiceTest < ActiveSupport::TestCase
     invoice = @invoice.dup
     invoice.buyer_vat_no = nil
     invoice.buyer = registrar
-    invoice.invoice_items = @invoice.invoice_items
+    invoice.items = @invoice.items
     invoice.save!
     assert_equal 'US1234', invoice.buyer_vat_no
   end
-end
+
+  def test_invalid_without_invoice_items
+    @invoice.items.clear
+    assert @invoice.invalid?
+  end
+
+  def test_iterates_over_invoice_items
+    invoice = Invoice.new(items: [InvoiceItem.new(description: 'test')])
+
+    iteration_count = 0
+    invoice.each do |invoice_item|
+      assert_equal 'test', invoice_item.description
+      iteration_count += 1
+    end
+
+    assert_equal 1, iteration_count
+  end
+end