Optionally use an on-disk sqlite db in tests

changelog.d/11702.misc

@@ -0,0 +1 @@
+Add the option to write sqlite test dbs to disk when running tests.

tests/server.py

@@ -14,6 +14,7 @@
 import hashlib
 import json
 import logging
+import os
 import time
 import uuid
 import warnings
@@ -71,6 +72,7 @@
     POSTGRES_HOST,
     POSTGRES_PASSWORD,
     POSTGRES_USER,
+    SQLITE_TEST_DB_LOCATION,
     USE_POSTGRES_FOR_TESTS,
     MockClock,
     default_config,
@@ -739,9 +741,16 @@ def setup_test_homeserver(
             },
         }
     else:
+        if SQLITE_TEST_DB_LOCATION != ":memory:":
+            # nuke the DB on disk
+            try:
+                os.remove(SQLITE_TEST_DB_LOCATION)
+            except FileNotFoundError:
+                pass
+
         database_config = {
             "name": "sqlite3",
-            "args": {"database": ":memory:", "cp_min": 1, "cp_max": 1},
+            "args": {"database": SQLITE_TEST_DB_LOCATION, "cp_min": 1, "cp_max": 1},
         }
 
     if "db_txn_limit" in kwargs:

tests/utils.py

@@ -42,6 +42,10 @@
 POSTGRES_PASSWORD = os.environ.get("SYNAPSE_POSTGRES_PASSWORD", None)
 POSTGRES_BASE_DB = "_synapse_unit_tests_base_%s" % (os.getpid(),)
 
+# When debugging a specific test, it's occasionally useful to write the
+# DB to /tmp and query it with the sqlite CLI.
+SQLITE_TEST_DB_LOCATION = os.environ.get("SYNAPSE_TEST_SQLITE_DB_LOCATION", ":memory:")
+
 # the dbname we will connect to in order to create the base database.
 POSTGRES_DBNAME_FOR_INITIAL_CREATE = "postgres"