Add a spec test that shows correct global resume token handling

Author: wilhuff

packages/firestore/test/unit/specs/listen_spec.test.ts

@@ -509,4 +509,30 @@ describeSpec('Listens:', [], () => {
       .watchAcksFull(query, 3000)
       .expectEvents(query, {});
   });
+
+  specTest('Persists global resume tokens', [], () => {
+    const query = Query.atPath(path('collection'));
+    const docA = doc('collection/a', 1000, { key: 'a' });
+
+    return (
+      spec()
+        .withGCEnabled(false)
+        .userListens(query)
+        .watchAcksFull(query, 1000, docA)
+        .expectEvents(query, { added: [docA] })
+
+        // Some time later, watch sends an updated resume token and the user stops
+        // listening.
+        .watchSnapshots(2000, [], 'resume-token-2000')
+        .userUnlistens(query)
+        .watchRemoves(query)
+
+        .userListens(query, 'resume-token-2000')
+        .expectEvents(query, { added: [docA], fromCache: true })
+        .watchAcks(query)
+        .watchCurrents(query, 'resume-token-3000')
+        .watchSnapshots(3000)
+        .expectEvents(query, { fromCache: false })
+    );
+  });
 });