Allow ExistentialDeposit = 0 (#6185)

* Allow ExistentialDeposit = 0

* there are better ways to check is an account exists

* fix StorageMapShim

* test account events and fix some bugs

substrate/frame/balances/src/tests_composite.rs

@@ -26,7 +26,7 @@ use sp_runtime::{
 };
 use sp_core::H256;
 use sp_io;
-use frame_support::{impl_outer_origin, parameter_types};
+use frame_support::{impl_outer_origin, impl_outer_event, parameter_types};
 use frame_support::traits::Get;
 use frame_support::weights::{Weight, DispatchInfo, IdentityFee};
 use std::cell::RefCell;
@@ -37,6 +37,17 @@ impl_outer_origin!{
 	pub enum Origin for Test {}
 }
 
+mod balances {
+	pub use crate::Event;
+}
+
+impl_outer_event! {
+	pub enum Event for Test {
+		system<T>,
+		balances<T>,
+	}
+}
+
 thread_local! {
 	static EXISTENTIAL_DEPOSIT: RefCell<u64> = RefCell::new(0);
 }
@@ -65,7 +76,7 @@ impl frame_system::Trait for Test {
 	type AccountId = u64;
 	type Lookup = IdentityLookup<Self::AccountId>;
 	type Header = Header;
-	type Event = ();
+	type Event = Event;
 	type BlockHashCount = BlockHashCount;
 	type MaximumBlockWeight = MaximumBlockWeight;
 	type DbWeight = ();
@@ -93,7 +104,7 @@ impl pallet_transaction_payment::Trait for Test {
 impl Trait for Test {
 	type Balance = u64;
 	type DustRemoval = ();
-	type Event = ();
+	type Event = Event;
 	type ExistentialDeposit = ExistentialDeposit;
 	type AccountStore = system::Module<Test>;
 }
@@ -138,7 +149,10 @@ impl ExtBuilder {
 				vec![]
 			},
 		}.assimilate_storage(&mut t).unwrap();
-		t.into()
+
+		let mut ext = sp_io::TestExternalities::new(t);
+		ext.execute_with(|| System::set_block_number(1));
+		ext
 	}
 }