Add Helpdesk issue API include serializer

tests/redmine_contacts_helpdesk/test_issue_api_serializer.rb

@@ -0,0 +1,46 @@
+require 'minitest/autorun'
+require_relative '../../plugins/redmine_contacts_helpdesk/lib/redmine_helpdesk/issue_api_serializer'
+
+Contact = Struct.new(:id, :name, :company, :primary_email, :emails, keyword_init: true)
+Ticket = Struct.new(:id, :contact_id, :message_id, :source, :from_address, :to_address, :cc_address, :ticket_date, :customer, keyword_init: true) do
+  def is_incoming?
+    true
+  end
+end
+Issue = Struct.new(:helpdesk_ticket, keyword_init: true)
+
+class IssueApiSerializerTest < Minitest::Test
+  def test_serializes_helpdesk_ticket_with_expanded_contact
+    contact = Contact.new(
+      :id => 1890,
+      :name => 'Callum Mackeonis',
+      :company => 'SafeTag Tracking',
+      :primary_email => 'callum@safetagtracking.com',
+      :emails => ['callum@safetagtracking.com']
+    )
+    ticket = Ticket.new(
+      :id => 35159,
+      :contact_id => 1890,
+      :message_id => 'message-id',
+      :source => 0,
+      :from_address => 'callum@safetagtracking.com',
+      :to_address => 'contact@ldrprep.com',
+      :cc_address => '',
+      :ticket_date => Time.utc(2026, 4, 14, 10, 18, 38),
+      :customer => contact
+    )
+
+    payload = RedmineHelpdesk::IssueApiSerializer.serialize(Issue.new(:helpdesk_ticket => ticket))
+
+    assert_equal 35159, payload[:id]
+    assert_equal 1890, payload[:contact_id]
+    assert_equal 'callum@safetagtracking.com', payload[:contact][:email]
+    assert_equal 'Callum Mackeonis', payload[:contact][:name]
+    assert_equal 'SafeTag Tracking', payload[:contact][:company]
+    assert_equal '2026-04-14T10:18:38Z', payload[:ticket_date]
+  end
+
+  def test_returns_nil_for_non_helpdesk_issue
+    assert_nil RedmineHelpdesk::IssueApiSerializer.serialize(Issue.new(:helpdesk_ticket => nil))
+  end
+end