Add test to ensure redis integration disabled unless installed

tests/test_api.py

@@ -1,3 +1,5 @@
+import pytest
+
 from sentry_sdk import (
     configure_scope,
     continue_trace,
@@ -7,12 +9,20 @@
     start_transaction,
 )
 from sentry_sdk.hub import Hub
+from sentry_sdk.integrations.redis import RedisIntegration
 
 try:
     from unittest import mock  # python 3.3 and above
 except ImportError:
     import mock  # python < 3.3
 
+try:
+    import redis  # noqa: F401
+except ImportError:
+    REDIS_INSTALLED = False
+else:
+    REDIS_INSTALLED = True
+
 
 def test_get_current_span():
     fake_hub = mock.MagicMock()
@@ -113,3 +123,10 @@ def test_continue_trace(sentry_init):
         assert propagation_context["dynamic_sampling_context"] == {
             "trace_id": "566e3688a61d4bc888951642d6f14a19"
         }
+
+
+@pytest.mark.skipif(REDIS_INSTALLED, reason="skipping because redis is installed")
+def test_redis_disabled_when_not_installed(sentry_init):
+    sentry_init()
+
+    assert Hub.current.get_integration(RedisIntegration) is None