Add test for money filter + streamline rounding error protection logic (#3714)

* add test cases

* use rounding protection only for currencies with <2 decimal places

* add more test cases

* use parameterized tests

src/pretix/base/templatetags/money.py

@@ -48,11 +48,18 @@ def money_filter(value: Decimal, arg='', hide_currency=False):
     places = settings.CURRENCY_PLACES.get(arg, 2)
     rounded = value.quantize(Decimal('1') / 10 ** places, ROUND_HALF_UP)
     if places < 2 and rounded != value:
-        places = 2
+        # We display decimal places even if we shouldn't for this currency if rounding
+        # would make the numbers incorrect. If this branch executes, it's likely a bug in
+        # pretix, but we won't show wrong numbers!
+        if hide_currency:
+            return floatformat(value, 2)
+        else:
+            return '{} {}'.format(arg, floatformat(value, 2))
+
     if hide_currency:
         return floatformat(value, places)
 
-    locale_parts = translation.get_language().split('-', 1)
+    locale_parts = translation.get_language().split("-", 1)
     locale = locale_parts[0]
     if len(locale_parts) > 1 and len(locale_parts[1]) == 2:
         try:
@@ -61,20 +68,9 @@ def money_filter(value: Decimal, arg='', hide_currency=False):
             pass
 
     try:
-        if rounded != value:
-            # We display decimal places even if we shouldn't for this currency if rounding
-            # would make the numbers incorrect. If this branch executes, it's likely a bug in
-            # pretix, but we won't show wrong numbers!
-            return '{} {}'.format(
-                arg,
-                floatformat(value, 2)
-            )
         return format_currency(value, arg, locale=locale)
     except:
-        return '{} {}'.format(
-            arg,
-            floatformat(value, places)
-        )
+        return '{} {}'.format(arg, floatformat(value, places))
 
 
 @register.filter("money_numberfield")