Force connection pool reset before running db tz tests [ci drivers]

It's possible that database connections checked back into the pool
could still have session timezones associated with them. This can
cause the database timezone tests to failure. This will reset the
connection pool before the test runs to ensure that doesn't happen.

test/metabase/driver/oracle_test.clj

@@ -5,8 +5,13 @@
             [metabase.driver
              [generic-sql :as sql]
              [oracle :as oracle]]
-            [metabase.models.setting :as setting]
-            [metabase.test.data.datasets :refer [expect-with-engine]]
+            [metabase.models
+             [database :refer [Database]]
+             [setting :as setting]]
+            [metabase.test.data :as data]
+            [metabase.test.data
+             [dataset-definitions :as defs]
+             [datasets :refer [expect-with-engine]]]
             [metabase.test.util :as tu])
   (:import metabase.driver.oracle.OracleDriver))
 
@@ -68,6 +73,4 @@
 
 (expect-with-engine :oracle
   "UTC"
-  (do
-    (setting/set! :report-timezone "")
-    (tu/db-timezone-id)))
+  (tu/db-timezone-id))

test/metabase/test/util.clj

@@ -10,6 +10,7 @@
              [driver :as driver]
              [task :as task]
              [util :as u]]
+            [metabase.driver.generic-sql :as sql]
             [metabase.models
              [card :refer [Card]]
              [collection :refer [Collection]]
@@ -436,16 +437,27 @@
                                   {:cron-schedule (.getCronExpression ^CronTrigger trigger)
                                    :data          (into {} (.getJobDataMap trigger))}))))}))))))
 
+(defn- clear-connection-pool
+  "It's possible that a previous test ran and set the session's timezone to something, then returned the session to
+  the pool. Sometimes that connection's session can remain intact and subsequent queries will continue in that
+  timezone. That causes problems for tests that we can determine the database's timezone. This function will reset the
+  connections in the connection pool for `db` to ensure that we get fresh session with no timezone specified"
+  [db]
+  (when-let [conn-pool (:datasource (sql/db->pooled-connection-spec db))]
+    (.softResetAllUsers conn-pool)))
+
 (defn db-timezone-id
   "Return the timezone id from the test database. Must be called with `metabase.test.data.datasets/*driver*` bound,
   such as via `metabase.test.data.datasets/with-engine`"
   []
   (assert (bound? #'*driver*))
-  (data/dataset test-data
-    (-> (driver/current-db-time *driver* (data/db))
-        .getChronology
-        .getZone
-        .getID)))
+  (let [db (data/db)]
+    (clear-connection-pool db)
+    (data/dataset test-data
+      (-> (driver/current-db-time *driver* db)
+          .getChronology
+          .getZone
+          .getID))))
 
 (defn call-with-jvm-tz
   "Invokes the thunk `F` with the JVM timezone set to `DTZ`, puts the various timezone settings back the way it found