Fix `has-user-setup` Setting not being cached correctly (#26841)

* Fix `has-user-setup` Setting not being cached correctly

* Fix Kondo error

src/metabase/setup.clj

 (ns metabase.setup
-  (:require [environ.core :as env]
-            [metabase.models.setting :as setting :refer [defsetting Setting]]
-            [metabase.models.user :refer [User]]
-            [toucan.db :as db])
-  (:import java.util.UUID))
+  (:require
+   [environ.core :as env]
+   [metabase.db.connection :as mdb.connection]
+   [metabase.models.setting :as setting :refer [defsetting Setting]]
+   [metabase.models.user :refer [User]]
+   [toucan.db :as db])
+  (:import
+   (java.util UUID)))
 
 (defsetting setup-token
   "A token used to signify that an instance has permissions to create the initial User. This is created upon the first
@@ -39,8 +42,13 @@
   ;; Once a User is created it's impossible for this to ever become falsey -- deleting the last User is disallowed.
   ;; After this returns true once the result is cached and it will continue to return true forever without any
   ;; additional DB hits.
-  :getter     (fn []
-                (let [user-exists? (atom false)]
-                  (or @user-exists?
-                      (reset! user-exists? (db/exists? User)))))
+  ;;
+  ;; This is keyed by the unique identifier for the application database, to support resetting it in tests or swapping
+  ;; it out in the REPL
+  :getter     (let [app-db-id->user-exists? (atom {})]
+                (fn []
+                  (or (get @app-db-id->user-exists? (mdb.connection/unique-identifier))
+                      (let [exists? (db/exists? User)]
+                        (swap! app-db-id->user-exists? assoc (mdb.connection/unique-identifier) exists?)
+                        exists?))))
   :doc        false)

test/metabase/setup_test.clj

+(ns metabase.setup-test
+  (:require
+   [clojure.test :refer :all]
+   [metabase.db :as mdb]
+   [metabase.db.schema-migrations-test.impl
+    :as schema-migrations-test.impl]
+   [metabase.setup :as setup]
+   [metabase.test :as mt]
+   [toucan.db :as db]))
+
+(deftest has-user-setup-cached-test
+  (testing "The has-user-setup getter should cache truthy results since it can never become falsey"
+    ;; make sure some test users are created.
+    (mt/initialize-if-needed! :test-users)
+    (db/with-call-counting [call-count]
+      ;; call has-user-setup several times.
+      (dotimes [_ 5]
+        (is (= true
+               (setup/has-user-setup))))
+      ;; `has-user-setup` should have done at most one application database call, as opposed to one call per call to
+      ;; the getter
+      (is (contains? #{0 1} (call-count)))))
+  (testing "Return falsey for an empty instance. Values should be cached for current app DB to support swapping in tests/REPL"
+    ;; create a new completely empty database.
+    (schema-migrations-test.impl/with-temp-empty-app-db [_conn :h2]
+      ;; make sure the DB is setup (e.g., run all the Liquibase migrations)
+      (mdb/setup-db!)
+      (db/with-call-counting [call-count]
+        (dotimes [_ 5]
+          (is (= false
+                 (setup/has-user-setup))))
+        (testing "Should continue doing new DB calls as long as there is no User"
+          (is (= 5
+                 (call-count)))))))
+  (testing "Switch back to the 'normal' app DB; value should still be cached for it"
+    (db/with-call-counting [call-count]
+      (is (= true
+             (setup/has-user-setup)))
+      (is (zero? (call-count))))))