fix: testnet cli command update genesis supply (cosmos#9497)

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## Description

closes: cosmos#9372 

<!-- Add a description of the changes that this PR introduces and the files that
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### This PR makes the `testnet` command update the bank genesis supply. 

When using the `testnet` cli command, it creates nodes and balances, but does **not** update the supply. When using this in conjunction with `add-genesis-account` which **does** update the supply, it creates an invalid genesis file. This PR updates the testnet command to properly set the supply.

---

### Author Checklist

*All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.*

I have...

- [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [x] added `!` to the type prefix if API or client breaking change
- [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [x] provided a link to the relevant issue or specification
- [x] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [x] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

*All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

simd/cmd/testnet.go

@@ -289,7 +289,10 @@ func initGenFiles(
 	var bankGenState banktypes.GenesisState
 	clientCtx.Codec.MustUnmarshalJSON(appGenState[banktypes.ModuleName], &bankGenState)
 
-	bankGenState.Balances = genBalances
+	bankGenState.Balances = banktypes.SanitizeGenesisBalances(genBalances)
+	for _, bal := range bankGenState.Balances {
+		bankGenState.Supply = bankGenState.Supply.Add(bal.Coins...)
+	}
 	appGenState[banktypes.ModuleName] = clientCtx.Codec.MustMarshalJSON(&bankGenState)
 
 	appGenStateJSON, err := json.MarshalIndent(appGenState, "", "  ")

simd/cmd/testnet_test.go

@@ -0,0 +1,50 @@
+package cmd
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"github.com/cosmos/cosmos-sdk/client"
+	"github.com/cosmos/cosmos-sdk/client/flags"
+	"github.com/cosmos/cosmos-sdk/server"
+	"github.com/cosmos/cosmos-sdk/simapp"
+	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
+	genutiltest "github.com/cosmos/cosmos-sdk/x/genutil/client/testutil"
+	genutiltypes "github.com/cosmos/cosmos-sdk/x/genutil/types"
+	"github.com/spf13/viper"
+	"github.com/stretchr/testify/require"
+	"github.com/tendermint/tendermint/libs/log"
+)
+
+func Test_TestnetCmd(t *testing.T) {
+	home := t.TempDir()
+	encodingConfig := simapp.MakeTestEncodingConfig()
+	logger := log.NewNopLogger()
+	cfg, err := genutiltest.CreateDefaultTendermintConfig(home)
+	require.NoError(t, err)
+
+	err = genutiltest.ExecInitCmd(simapp.ModuleBasics, home, encodingConfig.Marshaler)
+	require.NoError(t, err)
+
+	serverCtx := server.NewContext(viper.New(), cfg, logger)
+	clientCtx := client.Context{}.
+		WithCodec(encodingConfig.Marshaler).
+		WithHomeDir(home).
+		WithTxConfig(encodingConfig.TxConfig)
+
+	ctx := context.Background()
+	ctx = context.WithValue(ctx, server.ServerContextKey, serverCtx)
+	ctx = context.WithValue(ctx, client.ClientContextKey, &clientCtx)
+	cmd := testnetCmd(simapp.ModuleBasics, banktypes.GenesisBalancesIterator{})
+	cmd.SetArgs([]string{fmt.Sprintf("--%s=test", flags.FlagKeyringBackend), fmt.Sprintf("--output-dir=%s", home)})
+	err = cmd.ExecuteContext(ctx)
+	require.NoError(t, err)
+
+	genFile := cfg.GenesisFile()
+	appState, _, err := genutiltypes.GenesisStateFromGenFile(genFile)
+	require.NoError(t, err)
+
+	bankGenState := banktypes.GetGenesisStateFromAppState(encodingConfig.Marshaler, appState)
+	require.NotEmpty(t, bankGenState.Supply.String())
+}