diff --git a/zerver/lib/test_classes.py b/zerver/lib/test_classes.py
index da6e876481..751db3d84a 100644
--- a/zerver/lib/test_classes.py
+++ b/zerver/lib/test_classes.py
@@ -135,6 +135,22 @@ class ZulipTestCase(TestCase):
         elif 'HTTP_HOST' not in kwargs:
             kwargs['HTTP_HOST'] = Realm.host_for_subdomain(self.DEFAULT_SUBDOMAIN)
 
+        # set User-Agent
+        if 'HTTP_AUTHORIZATION' in kwargs:
+            # An API request; use mobile as the default user agent
+            default_user_agent = "ZulipMobile/26.22.145 (iOS 10.3.1)"
+        else:
+            # A webapp request; use a browser User-Agent string.
+            default_user_agent = ("Mozilla/5.0 (Windows NT 10.0; Win64; x64) " +
+                                  "AppleWebKit/537.36 (KHTML, like Gecko) " +
+                                  "Chrome/79.0.3945.130 Safari/537.36")
+        if kwargs.get('skip_user_agent'):
+            # Provide a way to disable setting User-Agent if desired.
+            assert 'HTTP_USER_AGENT' not in kwargs
+            del kwargs['skip_user_agent']
+        elif 'HTTP_USER_AGENT' not in kwargs:
+            kwargs['HTTP_USER_AGENT'] = default_user_agent
+
     @instrument_url
     def client_patch(self, url: str, info: Dict[str, Any]={}, **kwargs: Any) -> HttpResponse:
         """
diff --git a/zerver/tests/test_compatibility.py b/zerver/tests/test_compatibility.py
index 0fe675d093..7b9817ccee 100644
--- a/zerver/tests/test_compatibility.py
+++ b/zerver/tests/test_compatibility.py
@@ -78,7 +78,7 @@ class CompatibilityTest(ZulipTestCase):
     '''.strip().split('\n') if case]
 
     def test_compatibility_without_user_agent(self) -> None:
-        result = self.client_get("/compatibility")
+        result = self.client_get("/compatibility", skip_user_agent=True)
         self.assert_json_error(result, 'User-Agent header missing from request')
 
     def test_compatibility(self) -> None:
diff --git a/zerver/tests/test_subs.py b/zerver/tests/test_subs.py
index d0fd955d22..78edb95e2c 100644
--- a/zerver/tests/test_subs.py
+++ b/zerver/tests/test_subs.py
@@ -2443,7 +2443,7 @@ class SubscriptionAPITest(ZulipTestCase):
                     streams_to_sub,
                     dict(principals=ujson.dumps([user1.email, user2.email])),
                 )
-        self.assert_length(queries, 43)
+        self.assert_length(queries, 42)
 
         self.assert_length(events, 7)
         for ev in [x for x in events if x['event']['type'] not in ('message', 'stream')]:
@@ -2817,7 +2817,7 @@ class SubscriptionAPITest(ZulipTestCase):
         # Make sure Zephyr mirroring realms such as MIT do not get
         # any tornado subscription events
         self.assert_length(events, 0)
-        self.assert_length(queries, 8)
+        self.assert_length(queries, 7)
 
         events = []
         with tornado_redirected_to_list(events):
@@ -2843,7 +2843,7 @@ class SubscriptionAPITest(ZulipTestCase):
                 dict(principals=ujson.dumps([self.test_email])),
             )
         # Make sure we don't make O(streams) queries
-        self.assert_length(queries, 19)
+        self.assert_length(queries, 18)
 
     def test_subscriptions_add_for_principal(self) -> None:
         """
@@ -3232,7 +3232,7 @@ class SubscriptionAPITest(ZulipTestCase):
                 [new_streams[0]],
                 dict(principals=ujson.dumps([user1.email, user2.email])),
             )
-        self.assert_length(queries, 43)
+        self.assert_length(queries, 42)
 
         # Test creating private stream.
         with queries_captured() as queries:
diff --git a/zerver/tests/test_tornado.py b/zerver/tests/test_tornado.py
index 50e95ba01d..607229561a 100644
--- a/zerver/tests/test_tornado.py
+++ b/zerver/tests/test_tornado.py
@@ -37,6 +37,7 @@ class TornadoWebTestCase(AsyncHTTPTestCase, ZulipTestCase):
 
     def client_get(self, path: str, **kwargs: Any) -> HTTPResponse:
         self.add_session_cookie(kwargs)
+        kwargs['skip_user_agent'] = True
         self.set_http_headers(kwargs)
         if 'HTTP_HOST' in kwargs:
             kwargs['headers']['Host'] = kwargs['HTTP_HOST']
@@ -45,6 +46,7 @@ class TornadoWebTestCase(AsyncHTTPTestCase, ZulipTestCase):
 
     def fetch_async(self, method: str, path: str, **kwargs: Any) -> None:
         self.add_session_cookie(kwargs)
+        kwargs['skip_user_agent'] = True
         self.set_http_headers(kwargs)
         if 'HTTP_HOST' in kwargs:
             kwargs['headers']['Host'] = kwargs['HTTP_HOST']
@@ -57,6 +59,7 @@ class TornadoWebTestCase(AsyncHTTPTestCase, ZulipTestCase):
         )
 
     def client_get_async(self, path: str, **kwargs: Any) -> None:
+        kwargs['skip_user_agent'] = True
         self.set_http_headers(kwargs)
         self.fetch_async('GET', path, **kwargs)
 
@@ -78,7 +81,8 @@ class TornadoWebTestCase(AsyncHTTPTestCase, ZulipTestCase):
         kwargs['headers'] = headers
 
     def create_queue(self, **kwargs: Any) -> str:
-        response = self.client_get('/json/events?dont_block=true', subdomain="zulip")
+        response = self.client_get('/json/events?dont_block=true', subdomain="zulip",
+                                   skip_user_agent=True)
         self.assertEqual(response.code, 200)
         body = ujson.loads(response.body)
         self.assertEqual(body['events'], [])