fix(fungible): remove BurnCoins usage (#1088)

* remove burn

* add unit tests

* typo

* fix test

testutil/sample/sample.go

@@ -37,7 +37,14 @@ func PubKey(r *rand.Rand) cryptotypes.PubKey {
 	return ed25519.GenPrivKeyFromSecret(seed).PubKey()
 }
 
-// AccAddress returns a sample account address
+// Bech32AccAddress returns a sample account address
+func Bech32AccAddress() sdk.AccAddress {
+	pk := ed25519.GenPrivKey().PubKey()
+	addr := pk.Address()
+	return sdk.AccAddress(addr)
+}
+
+// AccAddress returns a sample account address in string
 func AccAddress() string {
 	pk := ed25519.GenPrivKey().PubKey()
 	addr := pk.Address()

x/fungible/keeper/zeta.go

@@ -4,44 +4,19 @@ import (
 	"math/big"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
-	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
 	"github.com/zeta-chain/zetacore/cmd/zetacored/config"
 	"github.com/zeta-chain/zetacore/x/fungible/types"
 )
 
 // MintZetaToEVMAccount mints ZETA (gas token) to the given address
+// NOTE: this method should be used with a temporary context, and it should not be committed if the method returns an error
 func (k *Keeper) MintZetaToEVMAccount(ctx sdk.Context, to sdk.AccAddress, amount *big.Int) error {
-	balanceCoin := k.bankKeeper.GetBalance(ctx, to, config.BaseDenom)
 	coins := sdk.NewCoins(sdk.NewCoin(config.BaseDenom, sdk.NewIntFromBigInt(amount)))
 	// Mint coins
 	if err := k.bankKeeper.MintCoins(ctx, types.ModuleName, coins); err != nil {
 		return err
 	}
 
 	// Send minted coins to the receiver
-	err := k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, to, coins)
-
-	if err == nil {
-		// Check expected receiver balance after transfer
-		balanceCoinAfter := k.bankKeeper.GetBalance(ctx, to, config.BaseDenom)
-		expCoin := balanceCoin.Add(coins[0])
-
-		if ok := balanceCoinAfter.IsEqual(expCoin); !ok {
-			err = sdkerrors.Wrapf(
-				types.ErrBalanceInvariance,
-				"invalid coin balance - expected: %v, actual: %v",
-				expCoin, balanceCoinAfter,
-			)
-		}
-	}
-
-	if err != nil {
-		// Revert minting if an error is found.
-		if err := k.bankKeeper.BurnCoins(ctx, types.ModuleName, coins); err != nil {
-			return err
-		}
-		return err
-	}
-
-	return nil
+	return k.bankKeeper.SendCoinsFromModuleToAccount(ctx, types.ModuleName, to, coins)
 }

x/fungible/keeper/zeta_test.go

@@ -0,0 +1,77 @@
+package keeper_test
+
+import (
+	"errors"
+	"math/big"
+	"testing"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/stretchr/testify/require"
+	"github.com/zeta-chain/zetacore/cmd/zetacored/config"
+	testkeeper "github.com/zeta-chain/zetacore/testutil/keeper"
+	"github.com/zeta-chain/zetacore/testutil/sample"
+	"github.com/zeta-chain/zetacore/x/fungible/types"
+)
+
+func TestKeeper_MintZetaToEVMAccount(t *testing.T) {
+	t.Run("should mint the token in the specified balance", func(t *testing.T) {
+		k, ctx, sdkk, _ := testkeeper.FungibleKeeper(t)
+		k.GetAuthKeeper().GetModuleAccount(ctx, types.ModuleName)
+
+		acc := sample.Bech32AccAddress()
+		bal := sdkk.BankKeeper.GetBalance(ctx, acc, config.BaseDenom)
+		require.True(t, bal.IsZero())
+
+		err := k.MintZetaToEVMAccount(ctx, acc, big.NewInt(42))
+		require.NoError(t, err)
+		bal = sdkk.BankKeeper.GetBalance(ctx, acc, config.BaseDenom)
+		require.True(t, bal.Amount.Equal(sdk.NewInt(42)))
+	})
+
+	coins42 := sdk.NewCoins(sdk.NewCoin(config.BaseDenom, sdk.NewInt(42)))
+
+	t.Run("should fail if minting fail", func(t *testing.T) {
+		k, ctx := testkeeper.FungibleKeeperAllMocks(t)
+
+		mockBankKeeper := testkeeper.GetFungibleBankMock(t, k)
+
+		mockBankKeeper.On(
+			"MintCoins",
+			ctx,
+			types.ModuleName,
+			coins42,
+		).Return(errors.New("error"))
+
+		err := k.MintZetaToEVMAccount(ctx, sample.Bech32AccAddress(), big.NewInt(42))
+		require.Error(t, err)
+
+		mockBankKeeper.AssertExpectations(t)
+	})
+
+	t.Run("should fail if sending coins fail", func(t *testing.T) {
+		k, ctx := testkeeper.FungibleKeeperAllMocks(t)
+		acc := sample.Bech32AccAddress()
+
+		mockBankKeeper := testkeeper.GetFungibleBankMock(t, k)
+
+		mockBankKeeper.On(
+			"MintCoins",
+			ctx,
+			types.ModuleName,
+			coins42,
+		).Return(nil)
+
+		mockBankKeeper.On(
+			"SendCoinsFromModuleToAccount",
+			ctx,
+			types.ModuleName,
+			acc,
+			coins42,
+		).Return(errors.New("error"))
+
+		err := k.MintZetaToEVMAccount(ctx, acc, big.NewInt(42))
+		require.Error(t, err)
+
+		mockBankKeeper.AssertExpectations(t)
+	})
+}