Feature/support mocking server timestamp

lib/src/fake_cloud_firestore_instance.dart

@@ -1,5 +1,6 @@
 import 'dart:convert';
 
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:cloud_firestore_platform_interface/cloud_firestore_platform_interface.dart'
     as firestore_interface;
@@ -35,11 +36,17 @@ class FakeFirebaseFirestore implements FirebaseFirestore {
   final BehaviorSubject<Map<String, dynamic>?> authObject =
       BehaviorSubject<Map<String, dynamic>?>();
   final FakeFirebaseSecurityRules securityRules;
+  final Clock _clock;
 
-  FakeFirebaseFirestore(
-      {Stream<Map<String, dynamic>?>? authObject, String? securityRules})
-      : securityRules =
-            FakeFirebaseSecurityRules(securityRules ?? allowAllDescription) {
+  Clock get clock => _clock;
+
+  FakeFirebaseFirestore({
+    Stream<Map<String, dynamic>?>? authObject,
+    String? securityRules,
+    Clock? clock,
+  })  : securityRules =
+            FakeFirebaseSecurityRules(securityRules ?? allowAllDescription),
+        _clock = clock ?? Clock() {
     // Wrap the Stream in a BehaviorSubject to access its latest value on
     // demand.
     authObject?.listen(this.authObject.add);

lib/src/mock_document_reference.dart

@@ -163,6 +163,10 @@ class MockDocumentReference<T extends Object?>
       final valueDelegate = FieldValuePlatform.getDelegate(value);
       final fieldValuePlatform = valueDelegate as MockFieldValuePlatform;
       final fieldValue = fieldValuePlatform.value;
+      // setup the fake Clock for FieldValueServerTimestamp
+      if (fieldValue is FieldValueServerTimestamp) {
+        fieldValue.clock = _firestore.clock;
+      }
       fieldValue.updateDocument(document, key);
     } else {
       document[key] = transformValue(value, timestampFromDateTime);

lib/src/mock_field_value_platform.dart

@@ -1,3 +1,4 @@
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore_platform_interface/cloud_firestore_platform_interface.dart';
 import 'package:fake_cloud_firestore/src/util.dart';
 import 'package:plugin_platform_interface/plugin_platform_interface.dart';
@@ -6,17 +7,27 @@ abstract class FakeFieldValue {
   const FakeFieldValue();
 
   static const delete = FieldValueDelete();
-  static const serverTimestamp = FieldValueServerTimestamp();
+  static final serverTimestamp = FieldValueServerTimestamp();
 
   void updateDocument(Map<String, dynamic> document, String key);
 }
 
 class FieldValueServerTimestamp extends FakeFieldValue {
-  const FieldValueServerTimestamp();
+  Clock? _clock;
+
+  set clock(Clock clock) {
+    _clock = clock;
+  }
+
+  Timestamp get now {
+    return Timestamp.fromDate(_clock?.now() ?? DateTime.now());
+  }
+
+  FieldValueServerTimestamp();
 
   @override
   void updateDocument(Map<String, dynamic> document, String key) {
-    document[key] = Timestamp.now();
+    document[key] = now;
   }
 }
 

pubspec.yaml

@@ -20,6 +20,7 @@ dependencies:
   fake_firebase_security_rules: ^0.5.2
   rx: ^0.3.0
   equatable: ^2.0.5
+  clock: ^1.1.1
 
 dev_dependencies:
   flutter_test:

test/fake_cloud_firestore_test.dart

@@ -1,3 +1,4 @@
+import 'package:clock/clock.dart';
 import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:fake_cloud_firestore/fake_cloud_firestore.dart';
 import 'package:flutter/services.dart';
@@ -683,6 +684,21 @@ void main() {
       expect(timeDiff, lessThan(1000));
     });
 
+    test('FieldValue.serverTimestamp() sets the time with fixed time',
+        () async {
+      final fixedTimestamp = Timestamp.fromMicrosecondsSinceEpoch(100);
+      final fakeClock = Clock.fixed(fixedTimestamp.toDate());
+      final firestore = FakeFirebaseFirestore(clock: fakeClock);
+      await firestore.collection('users').doc(uid).set({
+        'created': FieldValue.serverTimestamp(),
+      });
+      final users = await firestore.collection('users').get();
+      final bob = users.docs.first;
+      expect(bob.get('created'), isNotNull);
+      final bobCreated = bob.get('created') as Timestamp;
+      expect(bobCreated, fixedTimestamp);
+    });
+
     test('FieldValue.increment() increments number', () async {
       final firestore = FakeFirebaseFirestore();
       // Empty document before update