Add 'currency' option for company

- e.g. an external supplier might have a default currency
- Adds a form input which only allows selection of allowed currency codes
- Add unit testing for currency validation

InvenTree/company/tests.py

@@ -1,4 +1,5 @@
 from django.test import TestCase
+from django.core.exceptions import ValidationError
 
 import os
 
@@ -119,6 +120,30 @@ class CompanySimpleTest(TestCase):
         self.assertIsNone(m3x12.get_price_info(3))
         self.assertIsNotNone(m3x12.get_price_info(50))
 
+    def test_currency_validation(self):
+        """
+        Test validation for currency selection
+        """
+
+        # Create a company with a valid currency code (should pass)
+        company = Company.objects.create(
+            name='Test',
+            description='Toast',
+            currency='AUD',
+        )
+
+        company.full_clean()
+
+        # Create a company with an invalid currency code (should fail)
+        company = Company.objects.create(
+            name='test',
+            description='Toasty',
+            currency='XZY',
+        )
+
+        with self.assertRaises(ValidationError):
+            company.full_clean()
+
 
 class ContactSimpleTest(TestCase):