msglist test: Write tests for the rest of MessageListView

For the more recently-added functionality, we'd written tests
along the way.  But we didn't have tests for the logic we
built earlier, which is some of the most core functionality.
Add tests for all that logic too.

test/model/message_list_test.dart

@@ -1,7 +1,11 @@
+import 'dart:convert';
+
 import 'package:checks/checks.dart';
+import 'package:http/http.dart' as http;
 import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/model.dart';
+import 'package:zulip/api/model/narrow.dart';
 import 'package:zulip/api/route/messages.dart';
 import 'package:zulip/model/content.dart';
 import 'package:zulip/model/message_list.dart';
@@ -11,6 +15,7 @@ import 'package:zulip/model/store.dart';
 import '../api/fake_api.dart';
 import '../api/model/model_checks.dart';
 import '../example_data.dart' as eg;
+import '../stdlib_checks.dart';
 import 'content_checks.dart';
 
 void main() async {
@@ -58,6 +63,106 @@ void main() async {
     checkNotifiedOnce();
   }
 
+  void checkLastRequest({
+    required ApiNarrow narrow,
+    required String anchor,
+    bool? includeAnchor,
+    required int numBefore,
+    required int numAfter,
+  }) {
+    check(connection.lastRequest).isA<http.Request>()
+      ..method.equals('GET')
+      ..url.path.equals('/api/v1/messages')
+      ..url.queryParameters.deepEquals({
+        'narrow': jsonEncode(narrow),
+        'anchor': anchor,
+        if (includeAnchor != null) 'include_anchor': includeAnchor.toString(),
+        'num_before': numBefore.toString(),
+        'num_after': numAfter.toString(),
+      });
+  }
+
+  test('fetch', () async {
+    const narrow = AllMessagesNarrow();
+    prepare(narrow: narrow);
+    connection.prepare(json: newestResult(
+      foundOldest: false,
+      messages: List.generate(100, (i) => eg.streamMessage(id: 1000 + i)),
+    ).toJson());
+    final fetchFuture = model.fetch();
+    check(model).fetched.isFalse();
+    checkInvariants(model);
+
+    checkNotNotified();
+    await fetchFuture;
+    checkNotifiedOnce();
+    check(model).messages.length.equals(100);
+    checkLastRequest(
+      narrow: narrow.apiEncode(),
+      anchor: 'newest',
+      numBefore: 100,
+      numAfter: 10,
+    );
+  });
+
+  test('fetch, short history', () async {
+    prepare();
+    connection.prepare(json: newestResult(
+      foundOldest: true,
+      messages: List.generate(30, (i) => eg.streamMessage(id: 1000 + i)),
+    ).toJson());
+    await model.fetch();
+    checkNotifiedOnce();
+    check(model).messages.length.equals(30);
+  });
+
+  test('fetch, no messages found', () async {
+    prepare();
+    connection.prepare(json: newestResult(
+      foundOldest: true,
+      messages: [],
+    ).toJson());
+    await model.fetch();
+    checkNotifiedOnce();
+    check(model)
+      ..fetched.isTrue()
+      ..messages.isEmpty();
+  });
+
+  test('maybeAddMessage', () async {
+    final stream = eg.stream();
+    prepare(narrow: StreamNarrow(stream.streamId));
+    await prepareMessages(foundOldest: true, messages:
+      List.generate(30, (i) => eg.streamMessage(id: 1000 + i, stream: stream)));
+
+    check(model).messages.length.equals(30);
+    model.maybeAddMessage(eg.streamMessage(id: 1100, stream: stream));
+    checkNotifiedOnce();
+    check(model).messages.length.equals(31);
+  });
+
+  test('maybeAddMessage, not in narrow', () async {
+    final stream = eg.stream(streamId: 123);
+    prepare(narrow: StreamNarrow(stream.streamId));
+    await prepareMessages(foundOldest: true, messages:
+      List.generate(30, (i) => eg.streamMessage(id: 1000 + i, stream: stream)));
+
+    check(model).messages.length.equals(30);
+    final otherStream = eg.stream(streamId: 234);
+    model.maybeAddMessage(eg.streamMessage(id: 1100, stream: otherStream));
+    checkNotNotified();
+    check(model).messages.length.equals(30);
+  });
+
+  test('maybeAddMessage, before fetch', () async {
+    final stream = eg.stream();
+    prepare(narrow: StreamNarrow(stream.streamId));
+    model.maybeAddMessage(eg.streamMessage(id: 1100, stream: stream));
+    checkNotNotified();
+    check(model).fetched.isFalse();
+    checkInvariants(model);
+  });
+
   test('findMessageWithId', () async {
     prepare();
     await prepareMessages(foundOldest: true, messages: [
@@ -254,6 +359,29 @@ void main() async {
       });
     });
   });
+
+  test('reassemble', () async {
+    final stream = eg.stream();
+    prepare(narrow: StreamNarrow(stream.streamId));
+    await prepareMessages(foundOldest: true, messages:
+      List.generate(30, (i) => eg.streamMessage(id: 1000 + i, stream: stream)));
+    model.maybeAddMessage(eg.streamMessage(id: 1100, stream: stream));
+    checkNotifiedOnce();
+    check(model).messages.length.equals(31);
+
+    // Mess with model.contents, to simulate it having come from
+    // a previous version of the code.
+    final correctContent = parseContent(model.messages[0].content);
+    model.contents[0] = const ZulipContent(nodes: [
+      ParagraphNode(links: null, nodes: [TextNode('something outdated')])
+    ]);
+    check(model.contents[0]).not(it()..equalsNode(correctContent));
+
+    model.reassemble();
+    checkNotifiedOnce();
+    check(model).messages.length.equals(31);
+    check(model.contents[0]).equalsNode(correctContent);
+  });
 }
 
 void checkInvariants(MessageListView model) {