feat(x/precisebank): Add keeper methods for store (#1912)

- Add store methods to get/set/delete/etc account fractional balances & remainder amount
- Add invariants to ensure stored state is correct

x/precisebank/keeper/fractional_balance.go

@@ -0,0 +1,109 @@
+package keeper
+
+import (
+	"errors"
+	"fmt"
+
+	sdkmath "cosmossdk.io/math"
+	"github.com/cosmos/cosmos-sdk/store/prefix"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	"github.com/kava-labs/kava/x/precisebank/types"
+)
+
+// GetFractionalBalance returns the fractional balance for an address.
+func (k *Keeper) GetFractionalBalance(
+	ctx sdk.Context,
+	address sdk.AccAddress,
+) (sdkmath.Int, bool) {
+	store := prefix.NewStore(ctx.KVStore(k.storeKey), types.FractionalBalancePrefix)
+
+	bz := store.Get(types.FractionalBalanceKey(address))
+	if bz == nil {
+		return sdkmath.ZeroInt(), false
+	}
+
+	var bal sdkmath.Int
+	if err := bal.Unmarshal(bz); err != nil {
+		panic(fmt.Errorf("failed to unmarshal fractional balance: %w", err))
+	}
+
+	return bal, true
+}
+
+// SetFractionalBalance sets the fractional balance for an address.
+func (k *Keeper) SetFractionalBalance(
+	ctx sdk.Context,
+	address sdk.AccAddress,
+	amount sdkmath.Int,
+) {
+	if address.Empty() {
+		panic(errors.New("address cannot be empty"))
+	}
+
+	if amount.IsZero() {
+		k.DeleteFractionalBalance(ctx, address)
+		return
+	}
+
+	// Ensure the fractional balance is valid before setting it. Use the
+	// NewFractionalAmountFromInt wrapper to use its Validate() method.
+	if err := types.NewFractionalAmountFromInt(amount).Validate(); err != nil {
+		panic(fmt.Errorf("amount is invalid: %w", err))
+	}
+
+	store := prefix.NewStore(ctx.KVStore(k.storeKey), types.FractionalBalancePrefix)
+
+	amountBytes, err := amount.Marshal()
+	if err != nil {
+		panic(fmt.Errorf("failed to marshal fractional balance: %w", err))
+	}
+
+	store.Set(types.FractionalBalanceKey(address), amountBytes)
+}
+
+// DeleteFractionalBalance deletes the fractional balance for an address.
+func (k *Keeper) DeleteFractionalBalance(
+	ctx sdk.Context,
+	address sdk.AccAddress,
+) {
+	store := prefix.NewStore(ctx.KVStore(k.storeKey), types.FractionalBalancePrefix)
+	store.Delete(types.FractionalBalanceKey(address))
+}
+
+// IterateFractionalBalances iterates over all fractional balances in the store
+// and performs a callback function.
+func (k *Keeper) IterateFractionalBalances(
+	ctx sdk.Context,
+	cb func(address sdk.AccAddress, amount sdkmath.Int) (stop bool),
+) {
+	store := prefix.NewStore(ctx.KVStore(k.storeKey), types.FractionalBalancePrefix)
+
+	iterator := store.Iterator(nil, nil)
+	defer iterator.Close()
+
+	for ; iterator.Valid(); iterator.Next() {
+		address := sdk.AccAddress(iterator.Key())
+
+		var amount sdkmath.Int
+		if err := amount.Unmarshal(iterator.Value()); err != nil {
+			panic(fmt.Errorf("failed to unmarshal fractional balance: %w", err))
+		}
+
+		if cb(address, amount) {
+			break
+		}
+	}
+}
+
+// GetTotalSumFractionalBalances returns the sum of all fractional balances.
+func (k *Keeper) GetTotalSumFractionalBalances(ctx sdk.Context) sdkmath.Int {
+	sum := sdkmath.ZeroInt()
+
+	k.IterateFractionalBalances(ctx, func(_ sdk.AccAddress, amount sdkmath.Int) bool {
+		sum = sum.Add(amount)
+		return false
+	})
+
+	return sum
+}

x/precisebank/keeper/fractional_balance_test.go

@@ -0,0 +1,189 @@
+package keeper_test
+
+import (
+	"testing"
+
+	sdkmath "cosmossdk.io/math"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/stretchr/testify/require"
+
+	"github.com/kava-labs/kava/x/precisebank/types"
+)
+
+func TestSetGetFractionalBalance(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	addr := sdk.AccAddress([]byte("test-address"))
+
+	tests := []struct {
+		name        string
+		address     sdk.AccAddress
+		amount      sdkmath.Int
+		setPanicMsg string
+	}{
+		{
+			"valid - min amount",
+			addr,
+			sdkmath.NewInt(1),
+			"",
+		},
+		{
+			"valid - positive amount",
+			addr,
+			sdkmath.NewInt(100),
+			"",
+		},
+		{
+			"valid - max amount",
+			addr,
+			types.ConversionFactor().SubRaw(1),
+			"",
+		},
+		{
+			"valid - zero amount (deletes)",
+			addr,
+			sdkmath.ZeroInt(),
+			"",
+		},
+		{
+			"invalid - negative amount",
+			addr,
+			sdkmath.NewInt(-1),
+			"amount is invalid: non-positive amount -1",
+		},
+		{
+			"invalid - over max amount",
+			addr,
+			types.ConversionFactor(),
+			"amount is invalid: amount 1000000000000 exceeds max of 999999999999",
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.setPanicMsg != "" {
+				require.PanicsWithError(t, tt.setPanicMsg, func() {
+					k.SetFractionalBalance(ctx, tt.address, tt.amount)
+				})
+
+				return
+			}
+
+			require.NotPanics(t, func() {
+				k.SetFractionalBalance(ctx, tt.address, tt.amount)
+			})
+
+			// If its zero balance, check it was deleted
+			if tt.amount.IsZero() {
+				_, exists := k.GetFractionalBalance(ctx, tt.address)
+				require.False(t, exists)
+
+				return
+			}
+
+			gotAmount, exists := k.GetFractionalBalance(ctx, tt.address)
+			require.True(t, exists)
+			require.Equal(t, tt.amount, gotAmount)
+
+			// Delete balance
+			k.DeleteFractionalBalance(ctx, tt.address)
+
+			_, exists = k.GetFractionalBalance(ctx, tt.address)
+			require.False(t, exists)
+		})
+	}
+}
+
+func TestSetFractionalBalance_InvalidAddr(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	require.PanicsWithError(
+		t,
+		"address cannot be empty",
+		func() {
+			k.SetFractionalBalance(ctx, sdk.AccAddress{}, sdkmath.NewInt(100))
+		},
+		"setting balance with empty address should panic",
+	)
+}
+
+func TestSetFractionalBalance_ZeroDeletes(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	addr := sdk.AccAddress([]byte("test-address"))
+
+	// Set balance
+	k.SetFractionalBalance(ctx, addr, sdkmath.NewInt(100))
+
+	bal, exists := k.GetFractionalBalance(ctx, addr)
+	require.True(t, exists)
+	require.Equal(t, sdkmath.NewInt(100), bal)
+
+	// Set zero balance
+	k.SetFractionalBalance(ctx, addr, sdkmath.ZeroInt())
+
+	_, exists = k.GetFractionalBalance(ctx, addr)
+	require.False(t, exists)
+
+	// Set zero balance again on non-existent balance
+	require.NotPanics(
+		t,
+		func() {
+			k.SetFractionalBalance(ctx, addr, sdkmath.ZeroInt())
+		},
+		"deleting non-existent balance should not panic",
+	)
+}
+
+func TestIterateFractionalBalances(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	addrs := []sdk.AccAddress{}
+
+	for i := 1; i < 10; i++ {
+		addr := sdk.AccAddress([]byte{byte(i)})
+		addrs = append(addrs, addr)
+
+		// Set balance same as their address byte
+		k.SetFractionalBalance(ctx, addr, sdkmath.NewInt(int64(i)))
+	}
+
+	seenAddrs := []sdk.AccAddress{}
+
+	k.IterateFractionalBalances(ctx, func(addr sdk.AccAddress, bal sdkmath.Int) bool {
+		seenAddrs = append(seenAddrs, addr)
+
+		// Balance is same as first address byte
+		require.Equal(t, int64(addr.Bytes()[0]), bal.Int64())
+
+		return false
+	})
+
+	require.ElementsMatch(t, addrs, seenAddrs, "all addresses should be seen")
+}
+
+func TestGetAggregateSumFractionalBalances(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	// Set balances from 1 to 10
+	sum := sdkmath.ZeroInt()
+	for i := 1; i < 10; i++ {
+		addr := sdk.AccAddress([]byte{byte(i)})
+		amt := sdkmath.NewInt(int64(i))
+
+		sum = sum.Add(amt)
+
+		require.NotPanics(t, func() {
+			k.SetFractionalBalance(ctx, addr, amt)
+		})
+	}
+
+	gotSum := k.GetTotalSumFractionalBalances(ctx)
+	require.Equal(t, sum, gotSum)
+}

x/precisebank/keeper/invariants.go

@@ -1,6 +1,9 @@
 package keeper
 
 import (
+	"fmt"
+
+	sdkmath "cosmossdk.io/math"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/kava-labs/kava/x/precisebank/types"
 )
@@ -11,11 +14,110 @@ func RegisterInvariants(
 	k Keeper,
 	bk types.BankKeeper,
 ) {
+	ir.RegisterRoute(types.ModuleName, "balance-remainder-total", BalancedFractionalTotalInvariant(k))
+	ir.RegisterRoute(types.ModuleName, "valid-fractional-balances", ValidFractionalAmountsInvariant(k))
+	ir.RegisterRoute(types.ModuleName, "valid-remainder-amount", ValidRemainderAmountInvariant(k))
 }
 
 // AllInvariants runs all invariants of the X/precisebank module.
 func AllInvariants(k Keeper) sdk.Invariant {
 	return func(ctx sdk.Context) (string, bool) {
+		res, stop := BalancedFractionalTotalInvariant(k)(ctx)
+		if stop {
+			return res, stop
+		}
+
+		res, stop = ValidFractionalAmountsInvariant(k)(ctx)
+		if stop {
+			return res, stop
+		}
+
+		res, stop = ValidRemainderAmountInvariant(k)(ctx)
+		if stop {
+			return res, stop
+		}
+
 		return "", false
 	}
 }
+
+// ValidFractionalAmountsInvariant checks that all individual fractional
+// balances are valid.
+func ValidFractionalAmountsInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		var (
+			msg   string
+			count int
+		)
+
+		k.IterateFractionalBalances(ctx, func(addr sdk.AccAddress, amount sdkmath.Int) bool {
+			if err := types.NewFractionalAmountFromInt(amount).Validate(); err != nil {
+				count++
+				msg += fmt.Sprintf("\t%s has an invalid fractional amount of %s\n", addr, amount)
+			}
+
+			return false
+		})
+
+		broken := count != 0
+
+		return sdk.FormatInvariant(
+			types.ModuleName, "valid-fractional-balances",
+			fmt.Sprintf("amount of invalid fractional balances found %d\n%s", count, msg),
+		), broken
+	}
+}
+
+// ValidRemainderAmountInvariant checks that the remainder amount is valid.
+func ValidRemainderAmountInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		var (
+			msg    string
+			broken bool
+		)
+
+		remainderAmount := k.GetRemainderAmount(ctx)
+
+		if !remainderAmount.IsZero() {
+			// Only validate if non-zero, as zero is default value
+			if err := types.NewFractionalAmountFromInt(remainderAmount).Validate(); err != nil {
+				broken = true
+				msg = fmt.Sprintf("remainder amount is invalid: %s", err)
+			}
+		}
+
+		return sdk.FormatInvariant(
+			types.ModuleName, "valid-remainder-amount",
+			msg,
+		), broken
+	}
+}
+
+// BalancedFractionalTotalInvariant checks that the sum of fractional balances
+// and the remainder amount is divisible by the conversion factor without any
+// leftover amount.
+func BalancedFractionalTotalInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		fractionalBalSum := k.GetTotalSumFractionalBalances(ctx)
+		remainderAmount := k.GetRemainderAmount(ctx)
+
+		total := fractionalBalSum.Add(remainderAmount)
+		fractionalAmount := total.Mod(types.ConversionFactor())
+
+		broken := false
+		msg := ""
+
+		if !fractionalAmount.IsZero() {
+			broken = true
+			msg = fmt.Sprintf(
+				"(sum(FractionalBalances) + remainder) %% conversionFactor should be 0 but got %v",
+				fractionalAmount,
+			)
+		}
+
+		return sdk.FormatInvariant(
+			types.ModuleName, "balance-remainder-total",
+			msg,
+		), broken
+	}
+}

x/precisebank/keeper/invariants_test.go

@@ -0,0 +1,170 @@
+package keeper_test
+
+import (
+	"testing"
+
+	sdkmath "cosmossdk.io/math"
+	"github.com/cosmos/cosmos-sdk/store/prefix"
+	storetypes "github.com/cosmos/cosmos-sdk/store/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	"github.com/kava-labs/kava/x/precisebank/keeper"
+	"github.com/kava-labs/kava/x/precisebank/types"
+	"github.com/stretchr/testify/require"
+)
+
+func TestBalancedFractionalTotalInvariant(t *testing.T) {
+	var ctx sdk.Context
+	var k keeper.Keeper
+
+	tests := []struct {
+		name       string
+		setupFn    func()
+		wantBroken bool
+		wantMsg    string
+	}{
+		{
+			"valid - empty state",
+			func() {},
+			false,
+			"",
+		},
+		{
+			"valid - balances, 0 remainder",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2))
+			},
+			false,
+			"",
+		},
+		{
+			"valid - balances, non-zero remainder",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2).SubRaw(1))
+
+				k.SetRemainderAmount(ctx, sdkmath.OneInt())
+			},
+			false,
+			"",
+		},
+		{
+			"invalid - balances, 0 remainder",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2).SubRaw(1))
+			},
+			true,
+			"precisebank: balance-remainder-total invariant\n(sum(FractionalBalances) + remainder) % conversionFactor should be 0 but got 999999999999\n",
+		},
+		{
+			"invalid - invalid balances, non-zero (insufficient) remainder",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2).SubRaw(2))
+				k.SetRemainderAmount(ctx, sdkmath.OneInt())
+			},
+			true,
+			"precisebank: balance-remainder-total invariant\n(sum(FractionalBalances) + remainder) % conversionFactor should be 0 but got 999999999999\n",
+		},
+		{
+			"invalid - invalid balances, non-zero (excess) remainder",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2).SubRaw(2))
+				k.SetRemainderAmount(ctx, sdkmath.NewInt(5))
+			},
+			true,
+			"precisebank: balance-remainder-total invariant\n(sum(FractionalBalances) + remainder) % conversionFactor should be 0 but got 3\n",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Reset each time
+			tk := NewTestKeeper()
+			ctx, k = tk.ctx, tk.keeper
+
+			tt.setupFn()
+
+			invariantFn := keeper.BalancedFractionalTotalInvariant(k)
+			msg, broken := invariantFn(ctx)
+
+			if tt.wantBroken {
+				require.True(t, broken, "invariant should be broken but is not")
+				require.Equal(t, tt.wantMsg, msg)
+			} else {
+				require.False(t, broken, "invariant should not be broken but is")
+			}
+		})
+	}
+}
+
+func TestValidFractionalAmountsInvariant(t *testing.T) {
+	var ctx sdk.Context
+	var k keeper.Keeper
+	var storeKey storetypes.StoreKey
+
+	tests := []struct {
+		name       string
+		setupFn    func()
+		wantBroken bool
+		wantMsg    string
+	}{
+		{
+			"valid - empty state",
+			func() {},
+			false,
+			"",
+		},
+		{
+			"valid - valid balances",
+			func() {
+				k.SetFractionalBalance(ctx, sdk.AccAddress{1}, types.ConversionFactor().QuoRaw(2))
+				k.SetFractionalBalance(ctx, sdk.AccAddress{2}, types.ConversionFactor().QuoRaw(2))
+			},
+			false,
+			"",
+		},
+		{
+			"invalid - exceeds max balance",
+			func() {
+				// Requires manual store manipulation so it is unlikely to have
+				// invalid state in practice. SetFractionalBalance will validate
+				// before setting.
+				addr := sdk.AccAddress{1}
+				amount := types.ConversionFactor()
+
+				store := prefix.NewStore(ctx.KVStore(storeKey), types.FractionalBalancePrefix)
+
+				amountBytes, err := amount.Marshal()
+				require.NoError(t, err)
+
+				store.Set(types.FractionalBalanceKey(addr), amountBytes)
+			},
+			true,
+			"precisebank: valid-fractional-balances invariant\namount of invalid fractional balances found 1\n\tkava1qy0xn7za has an invalid fractional amount of 1000000000000\n\n",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Reset each time
+			tk := NewTestKeeper()
+			ctx, k, storeKey = tk.ctx, tk.keeper, tk.storeKey
+
+			tt.setupFn()
+
+			invariantFn := keeper.ValidFractionalAmountsInvariant(k)
+			msg, broken := invariantFn(ctx)
+
+			if tt.wantBroken {
+				require.True(t, broken, "invariant should be broken but is not")
+				require.Equal(t, tt.wantMsg, msg)
+			} else {
+				require.False(t, broken, "invariant should not be broken but is")
+			}
+		})
+	}
+}

x/precisebank/keeper/keeper_test.go

@@ -0,0 +1,36 @@
+package keeper_test
+
+import (
+	storetypes "github.com/cosmos/cosmos-sdk/store/types"
+	"github.com/cosmos/cosmos-sdk/testutil"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	"github.com/kava-labs/kava/app"
+	"github.com/kava-labs/kava/x/precisebank/keeper"
+	"github.com/kava-labs/kava/x/precisebank/types"
+)
+
+// testKeeper defines necessary fields for testing keeper store methods that
+// don't require a full app setup.
+type testKeeper struct {
+	ctx      sdk.Context
+	keeper   keeper.Keeper
+	storeKey *storetypes.KVStoreKey
+}
+
+func NewTestKeeper() testKeeper {
+	storeKey := sdk.NewKVStoreKey(types.ModuleName)
+	// Not required by module, but needs to be non-nil for context
+	tKey := sdk.NewTransientStoreKey("transient_test")
+	ctx := testutil.DefaultContext(storeKey, tKey)
+
+	tApp := app.NewTestApp()
+	cdc := tApp.AppCodec()
+	k := keeper.NewKeeper(cdc, storeKey)
+
+	return testKeeper{
+		ctx:      ctx,
+		keeper:   k,
+		storeKey: storeKey,
+	}
+}

x/precisebank/keeper/remainder_amount.go

@@ -0,0 +1,66 @@
+package keeper
+
+import (
+	"fmt"
+
+	sdkmath "cosmossdk.io/math"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	"github.com/kava-labs/kava/x/precisebank/types"
+)
+
+// GetRemainderAmount returns the internal remainder amount.
+func (k *Keeper) GetRemainderAmount(
+	ctx sdk.Context,
+) sdkmath.Int {
+	store := ctx.KVStore(k.storeKey)
+
+	bz := store.Get(types.RemainderBalanceKey)
+	if bz == nil {
+		return sdkmath.ZeroInt()
+	}
+
+	var bal sdkmath.Int
+	if err := bal.Unmarshal(bz); err != nil {
+		panic(fmt.Errorf("failed to unmarshal remainder amount: %w", err))
+	}
+
+	return bal
+}
+
+// SetRemainderAmount sets the internal remainder amount.
+func (k *Keeper) SetRemainderAmount(
+	ctx sdk.Context,
+	amount sdkmath.Int,
+) {
+	// Prevent storing zero amounts. In practice, the remainder amount should
+	// only be non-zero during transactions as mint and burns should net zero
+	// due to only being used for EVM transfers.
+	if amount.IsZero() {
+		k.DeleteRemainderAmount(ctx)
+		return
+	}
+
+	// Ensure the remainder is valid before setting it. Follows the same
+	// validation as FractionalBalance with the same value range.
+	if err := types.NewFractionalAmountFromInt(amount).Validate(); err != nil {
+		panic(fmt.Errorf("remainder amount is invalid: %w", err))
+	}
+
+	store := ctx.KVStore(k.storeKey)
+
+	amountBytes, err := amount.Marshal()
+	if err != nil {
+		panic(fmt.Errorf("failed to marshal remainder amount: %w", err))
+	}
+
+	store.Set(types.RemainderBalanceKey, amountBytes)
+}
+
+// DeleteRemainderAmount deletes the internal remainder amount.
+func (k *Keeper) DeleteRemainderAmount(
+	ctx sdk.Context,
+) {
+	store := ctx.KVStore(k.storeKey)
+	store.Delete(types.RemainderBalanceKey)
+}

x/precisebank/keeper/remainder_amount_test.go

@@ -0,0 +1,71 @@
+package keeper_test
+
+import (
+	"testing"
+
+	sdkmath "cosmossdk.io/math"
+	"github.com/kava-labs/kava/x/precisebank/types"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetSetRemainderAmount(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k, storeKey := tk.ctx, tk.keeper, tk.storeKey
+
+	// Set amount
+	k.SetRemainderAmount(ctx, sdkmath.NewInt(100))
+
+	amt := k.GetRemainderAmount(ctx)
+	require.Equal(t, sdkmath.NewInt(100), amt)
+
+	// Set zero balance
+	k.SetRemainderAmount(ctx, sdkmath.ZeroInt())
+
+	amt = k.GetRemainderAmount(ctx)
+	require.Equal(t, sdkmath.ZeroInt(), amt)
+
+	// Get directly from store to make sure it was actually deleted
+	store := ctx.KVStore(storeKey)
+	bz := store.Get(types.RemainderBalanceKey)
+	require.Nil(t, bz)
+}
+
+func TestInvalidRemainderAmount(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k := tk.ctx, tk.keeper
+
+	// Set negative amount
+	require.PanicsWithError(t, "remainder amount is invalid: non-positive amount -1", func() {
+		k.SetRemainderAmount(ctx, sdkmath.NewInt(-1))
+	})
+
+	// Set amount over max
+	require.PanicsWithError(t, "remainder amount is invalid: amount 1000000000000 exceeds max of 999999999999", func() {
+		k.SetRemainderAmount(ctx, types.ConversionFactor())
+	})
+}
+
+func TestDeleteRemainderAmount(t *testing.T) {
+	tk := NewTestKeeper()
+	ctx, k, storeKey := tk.ctx, tk.keeper, tk.storeKey
+
+	require.NotPanics(t, func() {
+		k.DeleteRemainderAmount(ctx)
+	})
+
+	// Set amount
+	k.SetRemainderAmount(ctx, sdkmath.NewInt(100))
+
+	amt := k.GetRemainderAmount(ctx)
+	require.Equal(t, sdkmath.NewInt(100), amt)
+
+	// Delete amount
+	k.DeleteRemainderAmount(ctx)
+
+	amt = k.GetRemainderAmount(ctx)
+	require.Equal(t, sdkmath.ZeroInt(), amt)
+
+	store := ctx.KVStore(storeKey)
+	bz := store.Get(types.RemainderBalanceKey)
+	require.Nil(t, bz)
+}

x/precisebank/types/fractional_amount.go

@@ -0,0 +1,41 @@
+package types
+
+import (
+	fmt "fmt"
+
+	sdkmath "cosmossdk.io/math"
+)
+
+// FractionalAmount represents a fractional amount between the valid range of 1
+// and maxFractionalAmount. This wraps an sdkmath.Int to provide additional
+// validation methods so it can be re-used in multiple places.
+type FractionalAmount struct {
+	sdkmath.Int
+}
+
+// NewFractionalAmountFromInt creates a new FractionalAmount from an sdkmath.Int.
+func NewFractionalAmountFromInt(i sdkmath.Int) FractionalAmount {
+	return FractionalAmount{i}
+}
+
+// NewFractionalAmount creates a new FractionalAmount from an int64.
+func NewFractionalAmount(i int64) FractionalAmount {
+	return FractionalAmount{sdkmath.NewInt(i)}
+}
+
+// Validate checks if the FractionalAmount is valid.
+func (f FractionalAmount) Validate() error {
+	if f.IsNil() {
+		return fmt.Errorf("nil amount")
+	}
+
+	if !f.IsPositive() {
+		return fmt.Errorf("non-positive amount %v", f)
+	}
+
+	if f.GT(maxFractionalAmount) {
+		return fmt.Errorf("amount %v exceeds max of %v", f, maxFractionalAmount)
+	}
+
+	return nil
+}

x/precisebank/types/fractional_balance.go

@@ -1,8 +1,6 @@
 package types
 
 import (
-	fmt "fmt"
-
 	sdkmath "cosmossdk.io/math"
 	sdk "github.com/cosmos/cosmos-sdk/types"
 )
@@ -40,17 +38,6 @@ func (fb FractionalBalance) Validate() error {
 		return err
 	}
 
-	if fb.Amount.IsNil() {
+	// Validate the amount with the FractionalAmount wrapper
-		return fmt.Errorf("nil amount")
+	return NewFractionalAmountFromInt(fb.Amount).Validate()
-	}
-
-	if !fb.Amount.IsPositive() {
-		return fmt.Errorf("non-positive amount %v", fb.Amount)
-	}
-
-	if fb.Amount.GT(maxFractionalAmount) {
-		return fmt.Errorf("amount %v exceeds max of %v", fb.Amount, maxFractionalAmount)
-	}
-
-	return nil
 }

x/precisebank/types/keys.go

@@ -1,5 +1,7 @@
 package types
 
+import sdk "github.com/cosmos/cosmos-sdk/types"
+
 const (
 	// ModuleName name that will be used throughout the module
 	ModuleName = "precisebank"
@@ -9,3 +11,18 @@ const (
 	// RouterKey Top level router key
 	RouterKey = ModuleName
 )
+
+// key prefixes for store
+var (
+	FractionalBalancePrefix = []byte{0x01} // address -> fractional balance
+)
+
+// Keys for store that are not prefixed
+var (
+	RemainderBalanceKey = []byte{0x02} // fractional balance remainder
+)
+
+// FractionalBalanceKey returns a key from an address
+func FractionalBalanceKey(address sdk.AccAddress) []byte {
+	return address.Bytes()
+}

x/precisebank/types/keys_test.go

@@ -0,0 +1,17 @@
+package types_test
+
+import (
+	"testing"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/kava-labs/kava/x/precisebank/types"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFractionalBalanceKey(t *testing.T) {
+	addr := sdk.AccAddress([]byte("test-address"))
+
+	key := types.FractionalBalanceKey(addr)
+	require.Equal(t, addr.Bytes(), key)
+	require.Equal(t, addr, sdk.AccAddress(key), "key should be able to be converted back to address")
+}