test: Add subscription helper in example data

Author: chrisbobbe

test/example_data.dart

@@ -123,6 +123,51 @@ ZulipStream stream({
 }
 const _stream = stream;
 
+Subscription subscription({
+  required ZulipStream stream,
+  bool? desktopNotifications,
+  bool? emailNotifications,
+  bool? wildcardMentionsNotify,
+  bool? pushNotifications,
+  bool? audibleNotifications,
+  bool? pinToTop,
+  String? emailAddress,
+  bool? isMuted,
+  bool? isWebPublic,
+  String? color,
+  int? streamPostPolicy,
+  int? messageRetentionDays,
+  bool? historyPublicToSubscribers,
+  int? firstMessageId,
+  int? streamWeeklyTraffic,
+  int? canRemoveSubscribersGroupId,
+}) {
+  return Subscription(
+    streamId: stream.streamId,
+    name: stream.name,
+    description: stream.description,
+    renderedDescription: stream.renderedDescription,
+    dateCreated: stream.dateCreated,
+    inviteOnly: stream.inviteOnly,
+    desktopNotifications: desktopNotifications ?? true,
+    emailNotifications: emailNotifications ?? true,
+    wildcardMentionsNotify: wildcardMentionsNotify ?? true,
+    pushNotifications: pushNotifications ?? true,
+    audibleNotifications: audibleNotifications ?? true,
+    pinToTop: pinToTop ?? true,
+    emailAddress: emailAddress ?? '[email protected]', // TODO generate example data
+    isMuted: isMuted ?? true,
+    isWebPublic: isWebPublic ?? true,
+    color: color ?? '#e79ab5',
+    streamPostPolicy: streamPostPolicy ?? 1,
+    messageRetentionDays: messageRetentionDays ?? 365,
+    historyPublicToSubscribers: historyPublicToSubscribers ?? true,
+    firstMessageId: firstMessageId ?? 123, // TODO generate example data
+    streamWeeklyTraffic: streamWeeklyTraffic ?? 100, // TODO generate example data
+    canRemoveSubscribersGroupId: canRemoveSubscribersGroupId ?? 123 // TODO generate example data
+  );
+}
+
 ////////////////////////////////////////////////////////////////
 // Messages, and pieces of messages.
 //