diff --git a/tests/utils.py b/tests/utils.py
index 260c2e91a2..41bf2d2e1b 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -54,13 +54,47 @@ POSTGRES_BASE_DB = "_synapse_unit_tests_base_%s" % (os.getpid(),)
 POSTGRES_DBNAME_FOR_INITIAL_CREATE = "postgres"
 
 
-def setupdb():
-    # If we're using PostgreSQL, set up the db once
-    if USE_POSTGRES_FOR_TESTS:
-        # create a PostgresEngine
-        db_engine = create_engine({"name": "psycopg2", "args": {}})
+def setupdb() -> None:
+    """
+    Set up a temporary database to run tests in. Only applicable to postgres,
+    which uses a persistent database server rather than a database in memory.
+    """
+    # Setting up the database is only required when using postgres
+    if not USE_POSTGRES_FOR_TESTS:
+        return
 
-        # connect to postgres to create the base database.
+    # create a PostgresEngine
+    db_engine = create_engine({"name": "psycopg2", "args": {}})
+
+    # connect to postgres to create the base database.
+    db_conn = db_engine.module.connect(
+        user=POSTGRES_USER,
+        host=POSTGRES_HOST,
+        password=POSTGRES_PASSWORD,
+        dbname=POSTGRES_DBNAME_FOR_INITIAL_CREATE,
+    )
+    db_conn.autocommit = True
+    cur = db_conn.cursor()
+    cur.execute("DROP DATABASE IF EXISTS %s;" % (POSTGRES_BASE_DB,))
+    cur.execute(
+        "CREATE DATABASE %s ENCODING 'UTF8' LC_COLLATE='C' LC_CTYPE='C' "
+        "template=template0;" % (POSTGRES_BASE_DB,)
+    )
+    cur.close()
+    db_conn.close()
+
+    # Set up in the db
+    db_conn = db_engine.module.connect(
+        database=POSTGRES_BASE_DB,
+        user=POSTGRES_USER,
+        host=POSTGRES_HOST,
+        password=POSTGRES_PASSWORD,
+    )
+    db_conn = LoggingDatabaseConnection(db_conn, db_engine, "tests")
+    prepare_database(db_conn, db_engine, None)
+    db_conn.close()
+
+    def _cleanup():
         db_conn = db_engine.module.connect(
             user=POSTGRES_USER,
             host=POSTGRES_HOST,
@@ -70,38 +104,10 @@ def setupdb():
         db_conn.autocommit = True
         cur = db_conn.cursor()
         cur.execute("DROP DATABASE IF EXISTS %s;" % (POSTGRES_BASE_DB,))
-        cur.execute(
-            "CREATE DATABASE %s ENCODING 'UTF8' LC_COLLATE='C' LC_CTYPE='C' "
-            "template=template0;" % (POSTGRES_BASE_DB,)
-        )
         cur.close()
         db_conn.close()
 
-        # Set up in the db
-        db_conn = db_engine.module.connect(
-            database=POSTGRES_BASE_DB,
-            user=POSTGRES_USER,
-            host=POSTGRES_HOST,
-            password=POSTGRES_PASSWORD,
-        )
-        db_conn = LoggingDatabaseConnection(db_conn, db_engine, "tests")
-        prepare_database(db_conn, db_engine, None)
-        db_conn.close()
-
-        def _cleanup():
-            db_conn = db_engine.module.connect(
-                user=POSTGRES_USER,
-                host=POSTGRES_HOST,
-                password=POSTGRES_PASSWORD,
-                dbname=POSTGRES_DBNAME_FOR_INITIAL_CREATE,
-            )
-            db_conn.autocommit = True
-            cur = db_conn.cursor()
-            cur.execute("DROP DATABASE IF EXISTS %s;" % (POSTGRES_BASE_DB,))
-            cur.close()
-            db_conn.close()
-
-        atexit.register(_cleanup)
+    atexit.register(_cleanup)
 
 
 def default_config(name: str) -> Dict[str, Any]: