Rename invoices.var_prc to vat_rate

#623

test/fixtures/invoices.yml

@@ -6,7 +6,7 @@ DEFAULTS: &DEFAULTS
   seller_name: John Doe
   seller_iban: 1234
   buyer_name: Jane Doe
-  vat_prc: 0.2
+  vat_rate: 0.2
 
 valid:
   <<: *DEFAULTS

test/models/invoice_test.rb

@@ -0,0 +1,9 @@
+require 'test_helper'
+
+class InvoiceTest < ActiveSupport::TestCase
+  def test_invalid_without_vat_rate
+    invoice = Invoice.new(vat_rate: nil)
+    invoice.validate
+    assert invoice.errors.added?(:vat_rate, :blank)
+  end
+end