add test

modal/app.py

@@ -124,6 +124,7 @@ def foo():
     """
 
     _all_apps: ClassVar[Dict[Optional[str], List["_App"]]] = {}
+    _container_app: ClassVar[Optional[RunningApp]] = None
 
     _name: Optional[str]
     _description: Optional[str]
@@ -141,8 +142,6 @@ def foo():
     _running_app: Optional[RunningApp]  # Various app info
     _client: Optional[_Client]
 
-    _container_app: ClassVar[Optional[RunningApp]] = None
-
     def __init__(
         self,
         name: Optional[str] = None,

test/conftest.py

@@ -192,6 +192,7 @@ def __init__(self, blob_host, blobs):
         self.volume_reloads: Dict[str, int] = defaultdict(lambda: 0)
 
         self.sandbox_defs = []
+        self.sandbox_app_id = None
         self.sandbox: asyncio.subprocess.Process = None
         self.sandbox_result: Optional[api_pb2.GenericResult] = None
 
@@ -1181,6 +1182,7 @@ async def SandboxCreate(self, stream):
             stdin=asyncio.subprocess.PIPE,
         )
 
+        self.sandbox_app_id = request.app_id
         self.sandbox_defs.append(request.definition)
 
         await stream.send_message(api_pb2.SandboxCreateResponse(sandbox_id="sb-123"))

test/container_test.py

@@ -2065,3 +2065,9 @@ def test_max_concurrency(servicer):
 
     outputs = [deserialize(item.result.data, ret.client) for item in ret.items]
     assert n_inputs in outputs
+
+
+@skip_github_non_linux
+def test_sandbox_infers_app(servicer, event_loop):
+    _run_container(servicer, "test.supports.sandbox", "spawn_sandbox")
+    assert servicer.sandbox_app_id == "ap-1"

test/supports/sandbox.py

@@ -0,0 +1,8 @@
+import modal
+
+app = modal.App()
+
+
+@app.function()
+def spawn_sandbox(x):
+    modal.Sandbox.create("bash", "-c", "echo bar")