test: Have eg.streamMessage and eg.dmMessage accept message content

Author: chrisbobbe

test/example_data.dart

@@ -103,10 +103,25 @@ Map<String, dynamic> _messagePropertiesFromSender(User? sender) {
   };
 }
 
+Map<String, dynamic> _messagePropertiesFromContent(String? content, String? contentMarkdown) {
+  if (contentMarkdown != null) {
+    assert(content == null);
+    return {
+      'content': contentMarkdown,
+      'content_type': 'text/x-markdown',
+    };
+  } else {
+    return {
+      'content': content ?? '<p>This is an example message.</p>',
+      'content_type': 'text/html',
+    };
+  }
+}
+
 const _stream = stream;
 
 StreamMessage streamMessage(
-    {User? sender, ZulipStream? stream, String? topic}) {
+    {User? sender, ZulipStream? stream, String? topic, String? content, String? contentMarkdown}) {
   final effectiveStream = stream ?? _stream();
   // The use of JSON here is convenient in order to delegate parts of the data
   // to helper functions.  The main downside is that it loses static typing
@@ -116,11 +131,9 @@ StreamMessage streamMessage(
   return StreamMessage.fromJson({
     ..._messagePropertiesBase,
     ..._messagePropertiesFromSender(sender),
+    ..._messagePropertiesFromContent(content, contentMarkdown),
     'display_recipient': effectiveStream.name,
     'stream_id': effectiveStream.streamId,
-
-    'content': '<p>This is an example stream message.</p>',
-    'content_type': 'text/html',
     'flags': [],
     'id': 1234567, // TODO generate example IDs
     'subject': topic ?? 'example topic',
@@ -133,17 +146,17 @@ StreamMessage streamMessage(
 ///
 /// See also:
 ///  * [streamMessage], to construct an example stream message.
-DmMessage dmMessage({required User from, required List<User> to}) {
+DmMessage dmMessage(
+    {required User from, required List<User> to, String? content, String? contentMarkdown}) {
   assert(!to.any((user) => user.userId == from.userId));
   return DmMessage.fromJson({
     ..._messagePropertiesBase,
     ..._messagePropertiesFromSender(from),
+    ..._messagePropertiesFromContent(content, contentMarkdown),
     'display_recipient': [from, ...to]
       .map((u) => {'id': u.userId, 'email': u.email, 'full_name': u.fullName})
       .toList(growable: false),
 
-    'content': '<p>This is an example DM.</p>',
-    'content_type': 'text/html',
     'flags': [],
     'id': 1234567, // TODO generate example IDs
     'subject': '',