Test that era offset works correctly

frame/staking/src/lib.rs

@@ -569,8 +569,6 @@ impl<T: Config> StakingLedger<T> {
 		let pre_slash_total = self.total;
 
 		let era_after_slash = slash_era + 1;
-		// TODO: test to make sure chunks before the slash are never slashed.
-		// at this era onwards, the funds can be slashed.
 		let chunk_unlock_era_after_slash = era_after_slash + T::BondingDuration::get();
 
 		// Calculate the total balance of active funds and unlocking funds in the affected range.

frame/staking/src/tests.rs

@@ -4850,6 +4850,19 @@ fn ledger_slash_works() {
 	assert_eq!(LedgerSlashPerEra::get().0, 0);
 	assert_eq!(LedgerSlashPerEra::get().1, BTreeMap::from([(4, 0), (5, 0)]));
 
+	// TODO test does not slash earlier eras
+	// Given
+	ledger.unlocking = bounded_vec![c(4, 100), c(5, 100), c(6, 100), c(7, 100)];
+	ledger.total = 4 * 100;
+	ledger.active = 0;
+	// When the first 2 chunks don't overlap with the affected range of unlock eras.
+	assert_eq!(ledger.slash(140, 0, 2), 140); // TODO
+										  // Then
+	assert_eq!(ledger.unlocking, vec![c(4, 100), c(5, 100), c(6, 30), c(7, 30)]);
+	assert_eq!(ledger.total, 4 * 100 - 140);
+	assert_eq!(LedgerSlashPerEra::get().0, 0);
+	assert_eq!(LedgerSlashPerEra::get().1, BTreeMap::from([(6, 30), (7, 30)]));
+
 	// Given
 	ledger.unlocking = bounded_vec![c(4, 40), c(5, 100), c(6, 10), c(7, 250)];
 	ledger.active = 500;