[vm] add a native test function for reading events

this is useful for ensuring that emitted events match expectations.

an increasingly large number of developers have become dependent on the
correctness of events. currently the only way to test events is at an
integration layer, which creates challenges for pure smart contract
teams. this change will improve their developer experience
substantially.

Author: davidiw

aptos-move/aptos-vm/src/natives.rs

@@ -76,7 +76,9 @@ pub fn assert_no_test_natives(err_msg: &str) {
                     && func_name.as_str() == "generate_keys_internal"
                 || module_name.as_str() == "bls12381" && func_name.as_str() == "sign_internal"
                 || module_name.as_str() == "bls12381"
-                    && func_name.as_str() == "generate_proof_of_possession_internal")
+                    && func_name.as_str() == "generate_proof_of_possession_internal"
+                || module_name.as_str() == "event"
+                    && func_name.as_str() == "emitted_events_internal")
         }),
         "{}",
         err_msg

aptos-move/framework/aptos-framework/sources/account.move

@@ -1309,4 +1309,27 @@ module aptos_framework::account {
         account_state.guid_creation_num = MAX_GUID_CREATION_NUM - 1;
         create_guid(account);
     }
+
+    #[test_only]
+    struct FakeCoin { }
+    #[test_only]
+    struct SadFakeCoin { }
+
+    #[test(account = @0x1234)]
+    fun test_events(account: &signer) acquires Account {
+        let addr = signer::address_of(account);
+        create_account_unchecked(addr);
+        register_coin<FakeCoin>(addr);
+
+        let eventhandle = &borrow_global<Account>(addr).coin_register_events;
+        let event = CoinRegisterEvent { type_info: type_info::type_of<FakeCoin>() };
+
+        let events = event::emitted_events(eventhandle);
+        assert!(vector::length(&events) == 1, 0);
+        assert!(vector::borrow(&events, 0) == &event, 1);
+        assert!(event::was_event_emitted(eventhandle, &event), 2);
+
+        let event = CoinRegisterEvent { type_info: type_info::type_of<SadFakeCoin>() };
+        assert!(!event::was_event_emitted(eventhandle, &event), 3);
+    }
 }

aptos-move/framework/aptos-framework/sources/event.move

@@ -54,4 +54,18 @@ module aptos_framework::event {
     public fun destroy_handle<T: drop + store>(handle: EventHandle<T>) {
         EventHandle<T> { counter: _, guid: _ } = handle;
     }
+
+    #[test_only]
+    public fun emitted_events<T: drop + store>(handle: &EventHandle<T>): vector<T> {
+        emitted_events_internal(bcs::to_bytes(&handle.guid))
+    }
+
+    #[test_only]
+    public fun was_event_emitted<T: drop + store>(handle: &EventHandle<T>, msg: &T): bool {
+        use std::vector;
+        vector::contains(&emitted_events(handle), msg)
+    }
+
+    #[test_only]
+    native fun emitted_events_internal<T: drop + store>(id: vector<u8>): vector<T>;
 }

aptos-move/framework/cached-packages/generated/head.mrb

@@ -68,6 +68,23 @@ pub fn make_native_write_to_event_store(
     }
 }
 
+#[cfg(feature = "testing")]
+fn native_emitted_events_internal(
+    _: &(),
+    context: &mut SafeNativeContext,
+    mut ty_args: Vec<Type>,
+    mut arguments: VecDeque<Value>,
+) -> SafeNativeResult<SmallVec<[Value; 1]>> {
+    debug_assert!(ty_args.len() == 1);
+    debug_assert!(arguments.len() == 1);
+
+    let ty = ty_args.pop().unwrap();
+    let guid = safely_pop_arg!(arguments, Vec<u8>);
+
+    let events = context.emitted_events(guid, ty)?;
+    Ok(smallvec![Value::vector_for_testing_only(events)])
+}
+
 /***************************************************************************************************
  * module
  *
@@ -77,21 +94,36 @@ pub struct GasParameters {
     pub write_to_event_store: WriteToEventStoreGasParameters,
 }
 
+#[allow(clippy::vec_init_then_push)]
 pub fn make_all(
     gas_params: GasParameters,
     calc_abstract_val_size: impl Fn(&Value) -> AbstractValueSize + Send + Sync + 'static,
     timed_features: TimedFeatures,
     features: Arc<Features>,
 ) -> impl Iterator<Item = (String, NativeFunction)> {
-    let natives = [(
+    let mut natives = vec![];
+
+    // Test-only natives
+    #[cfg(feature = "testing")]
+    natives.push((
+        "emitted_events_internal",
+        make_safe_native(
+            (),
+            timed_features.clone(),
+            features.clone(),
+            native_emitted_events_internal,
+        ),
+    ));
+
+    natives.push((
         "write_to_event_store",
         make_safe_native(
             gas_params.write_to_event_store,
             timed_features,
             features,
             make_native_write_to_event_store(calc_abstract_val_size),
         ),
-    )];
+    ));
 
     make_module_natives(natives)
 }