add failure test and final changes

chia/wallet/coin_selection.py

@@ -78,7 +78,7 @@ async def select_coins(
         log.debug(f"Selected all smaller coins because they equate to an exact match of the target.: {smaller_coins}")
         return set(smaller_coins)
     elif smaller_coin_sum < amount:
-        smallest_coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins, amount)
+        smallest_coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins)
         log.debug(f"Selected closest greater coin: {smallest_coin.name()}")
         return {smallest_coin}
     elif smaller_coin_sum > amount:
@@ -87,7 +87,7 @@ async def select_coins(
         if coin_set is None:
             raise ValueError("Knapsack algorithm failed to find a solution.")
         if len(coin_set) > max_num_coins:
-            coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins, amount)
+            coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins)
             if coin is None or coin.amount < amount:
                 raise ValueError(
                     "Can't make this transaction because the transaction would use over 500 "
@@ -97,13 +97,8 @@ async def select_coins(
         return coin_set
     else:
         # if we == amount and len(smaller_coins) >= max_num_coins.
-        coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins, amount)
+        coin = select_smallest_coin_over_target(len(smaller_coins), valid_spendable_coins)
         log.debug(f"Resorted to selecting smallest coin over target due to dust.: {coin}")
-        if coin is None or coin.amount < amount:
-            raise ValueError(
-                "Can't make this transaction because the transaction would use over 500 "
-                "coins which is unlikely to get confirmed. Try making a smaller transaction to condense the dust."
-            )
         return {coin}
 
 
@@ -119,9 +114,11 @@ def check_for_exact_match(coin_list: List[Coin], target: uint64) -> Optional[Coi
 
 
 # amount of coins smaller than target, followed by a list of all valid spendable coins sorted in descending order.
-def select_smallest_coin_over_target(
-    smaller_coin_amount: int, valid_spendable_coin_list: List[Coin], target_amount: uint128
-) -> Coin:
+def select_smallest_coin_over_target(smaller_coin_amount: int, valid_spendable_coin_list: List[Coin]) -> Coin:
+    if smaller_coin_amount >= len(valid_spendable_coin_list):
+        raise ValueError(
+            "There are no coins greater then the target. This is caused by having too many dust coins. Try making a smaller transaction to condense the dust."
+        )
     if smaller_coin_amount > 0:  # in case we only have bigger coins.
         greater_coins = valid_spendable_coin_list[:-smaller_coin_amount]
     else:

tests/wallet/test_coin_selection.py

@@ -110,6 +110,40 @@ async def test_coin_selection_with_dust(self, a_hash: bytes32) -> None:
             assert sum([coin.amount for coin in result]) >= target_amount
             assert len(result) <= 500
 
+    @pytest.mark.asyncio
+    async def test_coin_selection_failure(self, a_hash: bytes32) -> None:
+        spendable_amount = uint128(10000)
+        coin_list: List[WalletCoinRecord] = []
+        for i in range(10000):
+            coin_list.append(
+                WalletCoinRecord(
+                    Coin(a_hash, std_hash(i), uint64(1)), uint32(1), uint32(1), False, True, WalletType(0), 1
+                )
+            )
+        # make sure coins are not identical.
+        # test for failure
+        with pytest.raises(ValueError):
+            for target_amount in [10000, 9999]:
+                result: Set[Coin] = await select_coins(
+                    spendable_amount,
+                    DEFAULT_CONSTANTS.MAX_COIN_AMOUNT,
+                    coin_list,
+                    {},
+                    logging.getLogger("test"),
+                    uint128(target_amount),
+                )
+        # test not enough coin failure.
+        with pytest.raises(ValueError):
+            for target_amount in [10001, 20000]:
+                result: Set[Coin] = await select_coins(
+                    spendable_amount,
+                    DEFAULT_CONSTANTS.MAX_COIN_AMOUNT,
+                    coin_list,
+                    {},
+                    logging.getLogger("test"),
+                    uint128(target_amount),
+                )
+
     @pytest.mark.asyncio
     async def test_coin_selection(self, a_hash: bytes32) -> None:
         coin_amounts = [3, 6, 20, 40, 80, 150, 160, 203, 202, 201, 320]