message_list: reduce redundant arguments

Author: Komyyy

lib/widgets/message_list.dart

@@ -1370,19 +1370,19 @@ class DateText extends StatelessWidget {
       ),
       formatHeaderDate(
         zulipLocalizations,
-        DateTime.fromMillisecondsSinceEpoch(timestamp * 1000),
-        now: ZulipBinding.instance.now()));
+        DateTime.fromMillisecondsSinceEpoch(timestamp * 1000)));
   }
 }
 
 @visibleForTesting
 String formatHeaderDate(
   ZulipLocalizations zulipLocalizations,
-  DateTime dateTime, {
-  required DateTime now,
-}) {
-  assert(!dateTime.isUtc && !now.isUtc,
-    '`dateTime` and `now` need to be in local time.');
+  DateTime dateTime,
+) {
+  assert(!dateTime.isUtc,
+    '`dateTime` need to be in local time.');
+
+  final now = ZulipBinding.instance.now();
 
   if (dateTime.year == now.year &&
       dateTime.month == now.month &&

test/widgets/message_list_test.dart

@@ -1,6 +1,7 @@
 import 'dart:convert';
 
 import 'package:checks/checks.dart';
+import 'package:clock/clock.dart';
 import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -1421,7 +1422,6 @@ void main() {
 
   group('formatHeaderDate', () {
     final zulipLocalizations = GlobalLocalizations.zulipLocalizations;
-    final now = DateTime.parse("2023-01-10 12:00");
     final testCases = [
       ("2023-01-10 12:00", zulipLocalizations.today),
       ("2023-01-10 00:00", zulipLocalizations.today),
@@ -1436,8 +1436,10 @@ void main() {
     ];
     for (final (dateTime, expected) in testCases) {
       test('$dateTime returns $expected', () {
-        check(formatHeaderDate(zulipLocalizations, DateTime.parse(dateTime), now: now))
-          .equals(expected);
+        withClock(Clock.fixed(DateTime.parse("2023-01-10 12:00")), () {
+          check(formatHeaderDate(zulipLocalizations, DateTime.parse(dateTime)))
+            .equals(expected);
+        });
       });
     }
   });