Add SQLite for unit tests

test/settings.py

@@ -2,6 +2,14 @@
 
 from sage_validation.settings import *  # noqa: F403
 
-DATABASES = {
-    "default": DATABASES["default"],  # noqa: F405
-}
+if os.getenv("USE_SQLITE", "false").lower() == "true":  # noqa: F405
+    DATABASES = {
+        "default": {
+            "ENGINE": "django.db.backends.sqlite3",
+            "NAME": "sage_validation",
+        }
+    }
+else:
+    DATABASES = {
+        "default": DATABASES["default"],
+    }

tox.ini

@@ -6,6 +6,10 @@ deps =
     mypy
     ruff
     -r requirements.txt
+
+setenv =
+    USE_SQLITE = true
+
 commands =
     ruff check .
     mypy .