exampleData: Add eg.subscription and eg.makeSubscription().

Also demonstrate using them, to reduce boilerplate in the
newly-well-typed messageActionSheet tests.

Several values change, generally to a more representative value or
a default value.  One notable one is `in_home_view`: this means
"not muted", and so it's an important fact that its default is true.

[chris: cherry-picked from zulip#3946.]

src/__tests__/lib/exampleData.js

@@ -2,7 +2,14 @@
 import deepFreeze from 'deep-freeze';
 import { createStore } from 'redux';
 
-import type { CrossRealmBot, Message, PmRecipientUser, Stream, User } from '../../api/modelTypes';
+import type {
+  CrossRealmBot,
+  Message,
+  PmRecipientUser,
+  Stream,
+  Subscription,
+  User,
+} from '../../api/modelTypes';
 import type { Action, GlobalState, RealmState } from '../../reduxTypes';
 import type { Auth, Account, Outbox } from '../../types';
 import { ZulipVersion } from '../../utils/zulipVersion';
@@ -178,6 +185,24 @@ export const stream: Stream = makeStream({
   description: 'An example stream.',
 });
 
+export const makeSubscription = (args: { stream?: Stream } = {}): Subscription => {
+  const { stream: streamInner = stream } = args;
+  return deepFreeze({
+    ...streamInner,
+    color: '#123456',
+    in_home_view: true,
+    pin_to_top: false,
+    audible_notifications: false,
+    desktop_notifications: false,
+    email_address: '??? make this value representative before using in a test :)',
+    is_old_stream: true,
+    push_notifications: null,
+    stream_weekly_traffic: 84,
+  });
+};
+
+export const subscription: Subscription = makeSubscription();
+
 /* ========================================================================
  * Messages
  */

src/message/__tests__/messageActionSheet-test.js

@@ -31,20 +31,7 @@ const baseBackgroundData = deepFreeze({
   },
   mute: [['announce', 'stream events']],
   ownUser: eg.selfUser,
-  subscriptions: [
-    {
-      ...eg.makeStream(),
-      color: '#ffffff',
-      in_home_view: false,
-      pin_to_top: false,
-      audible_notifications: false,
-      desktop_notifications: false,
-      email_address: 'stream@email.com',
-      is_old_stream: false,
-      push_notifications: true,
-      stream_weekly_traffic: 2,
-    },
-  ],
+  subscriptions: [],
   theme: 'default',
   twentyFourHourTime: false,
 });
@@ -141,7 +128,7 @@ describe('constructHeaderActionButtons', () => {
 
     const subscriptions = deepFreeze([
       {
-        ...baseBackgroundData.subscriptions[0],
+        ...eg.subscription,
         name: 'electron issues',
         in_home_view: false,
       },
@@ -168,7 +155,7 @@ describe('constructHeaderActionButtons', () => {
 
     const subscriptions = deepFreeze([
       {
-        ...baseBackgroundData.subscriptions[0],
+        ...eg.subscription,
         name: 'electron issues',
         in_home_view: true,
       },