test(tvix/composition): add recursion and concurrent tests

Change-Id: Ic10773b08d940b45c3067bd514c3080cadac9606
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12003
Autosubmit: yuka <yuka@yuka.dev>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/castore/src/composition.rs

@@ -476,3 +476,66 @@ impl Composition {
         }
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::blobservice::BlobService;
+    use std::sync::Arc;
+
+    /// Test that we return a reference to the same instance of MemoryBlobService (via ptr_eq)
+    /// when instantiating the same entrypoint twice. By instantiating concurrently, we also
+    /// test the channels notifying the second consumer when the store has been instantiated.
+    #[tokio::test]
+    async fn concurrent() {
+        let blob_services_configs_json = serde_json::json!({
+            "default": {
+                "type": "memory",
+            }
+        });
+
+        let blob_services_configs =
+            with_registry(&REG, || serde_json::from_value(blob_services_configs_json)).unwrap();
+        let mut blob_service_composition = Composition::default();
+        blob_service_composition.extend_with_configs::<dyn BlobService>(blob_services_configs);
+        let (blob_service1, blob_service2) = tokio::join!(
+            blob_service_composition.build::<dyn BlobService>("default"),
+            blob_service_composition.build::<dyn BlobService>("default")
+        );
+        assert!(Arc::ptr_eq(
+            &blob_service1.unwrap(),
+            &blob_service2.unwrap()
+        ));
+    }
+
+    /// Test that we throw the correct error when an instantiation would recurse (deadlock)
+    #[tokio::test]
+    async fn reject_recursion() {
+        let blob_services_configs_json = serde_json::json!({
+            "default": {
+                "type": "combined",
+                "local": "other",
+                "remote": "other"
+            },
+            "other": {
+                "type": "combined",
+                "local": "default",
+                "remote": "default"
+            }
+        });
+
+        let blob_services_configs =
+            with_registry(&REG, || serde_json::from_value(blob_services_configs_json)).unwrap();
+        let mut blob_service_composition = Composition::default();
+        blob_service_composition.extend_with_configs::<dyn BlobService>(blob_services_configs);
+        match blob_service_composition
+            .build::<dyn BlobService>("default")
+            .await
+        {
+            Err(CompositionError::Recursion(stack)) => {
+                assert_eq!(stack, vec!["default".to_string(), "other".to_string()])
+            }
+            other => panic!("should have returned an error, returned: {:?}", other.err()),
+        }
+    }
+}