Some tests for invoice binding

app/models/bank_transaction.rb

@@ -1,3 +1,38 @@
 class BankTransaction < ActiveRecord::Base
   belongs_to :bank_statement
+  has_one :account_activity
+
+  scope :unbinded, -> { where('id NOT IN (SELECT bank_transaction_id FROM account_activities)') }
+
+  def binded?
+    account_activity.present?
+  end
+
+  # For successful binding, reference number, invoice id and sum must match with the invoice
+  # rubocop: disable Metrics/PerceivedComplexity
+  # rubocop: disable Metrics/CyclomaticComplexity
+  def bind_with_invoice
+    return if binded?
+    registrar = Registrar.find_by(reference_no: reference_no)
+    return unless registrar
+
+    match = description.match(/^[^\d]*(\d+)/)
+    return unless match
+
+    invoice_id = match[1].to_i
+    return unless invoice_id
+
+    invoice = registrar.invoices.find_by(id: invoice_id)
+    return unless invoice
+
+    return if invoice.sum != sum
+    create_account_activity(
+      account: registrar.cash_account,
+      invoice: invoice,
+      sum: sum,
+      currency: currency
+    )
+  end
+  # rubocop: enable Metrics/PerceivedComplexity
+  # rubocop: enable Metrics/CyclomaticComplexity
 end