Application Testnets

Building an application is complicated and requires a lot of testing. The Cosmos SDK provides a way to test your application in a real-world environment: a testnet.

We allow developers to take the state from their mainnet and run tests against the state. This is useful for testing upgrade migrations, or for testing the application in a real-world environment.

Testnet Setup

We will be breaking down the steps to create a testnet from mainnet state.

  // InitMerlinAppForTestnet is broken down into two sections:
  // Required Changes: Changes that, if not made, will cause the testnet to halt or panic
  // Optional Changes: Changes to customize the testnet to one's liking (lower vote times, fund accounts, etc)
  func InitMerlinAppForTestnet(app *MerlinApp, newValAddr bytes.HexBytes, newValPubKey crypto.PubKey, newOperatorAddress, upgradeToTrigger string) *MerlinApp {
  ...
  }

Required Changes

Staking

When creating a testnet the important part is migrate the validator set from many validators to one or a few. This allows developers to spin up the chain without needing to replace validator keys.

	ctx := app.BaseApp.NewUncachedContext(true, tmproto.Header{})
	pubkey := &ed25519.PubKey{Key: newValPubKey.Bytes()}
	pubkeyAny, err := types.NewAnyWithValue(pubkey)
	if err != nil {
		tmos.Exit(err.Error())
	}

	// STAKING
	//

	// Create Validator struct for our new validator.
	_, bz, err := bech32.DecodeAndConvert(newOperatorAddress)
	if err != nil {
		tmos.Exit(err.Error())
	}
	bech32Addr, err := bech32.ConvertAndEncode("simvaloper", bz)
	if err != nil {
		tmos.Exit(err.Error())
	}
	newVal := stakingtypes.Validator{
		OperatorAddress: bech32Addr,
		ConsensusPubkey: pubkeyAny,
		Jailed:          false,
		Status:          stakingtypes.Bonded,
		Tokens:          sdk.NewInt(900000000000000),
		DelegatorShares: sdk.MustNewDecFromStr("10000000"),
		Description: stakingtypes.Description{
			Moniker: "Testnet Validator",
		},
		Commission: stakingtypes.Commission{
			CommissionRates: stakingtypes.CommissionRates{
				Rate:          sdk.MustNewDecFromStr("0.05"),
				MaxRate:       sdk.MustNewDecFromStr("0.1"),
				MaxChangeRate: sdk.MustNewDecFromStr("0.05"),
			},
		},
		MinSelfDelegation: sdk.OneInt(),
	}

	// Remove all validators from power store
	stakingKey := app.GetKey(stakingtypes.ModuleName)
	stakingStore := ctx.KVStore(stakingKey)
	iterator := app.StakingKeeper.ValidatorsPowerStoreIterator(ctx)
	for ; iterator.Valid(); iterator.Next() {
		stakingStore.Delete(iterator.Key())
	}
	iterator.Close()

	// Remove all valdiators from last validators store
	iterator = app.StakingKeeper.LastValidatorsIterator(ctx)
	for ; iterator.Valid(); iterator.Next() {
		app.StakingKeeper.LastValidatorPower.Delete(iterator.Key())
	}
	iterator.Close()

	// Add our validator to power and last validators store
	app.StakingKeeper.SetValidator(ctx, newVal)
	err = app.StakingKeeper.SetValidatorByConsAddr(ctx, newVal)
	if err != nil {
		panic(err)
	}
	app.StakingKeeper.SetValidatorByPowerIndex(ctx, newVal)
	app.StakingKeeper.SetLastValidatorPower(ctx, newVal.GetOperator(), 0)
	if err := app.StakingKeeper.Hooks().AfterValidatorCreated(ctx, newVal.GetOperator()); err != nil {
		panic(err)
	}

Distribution

Since the validator set has changed, we need to update the distribution records for the new validator.

	// Initialize records for this validator across all distribution stores
	app.DistrKeeper.ValidatorHistoricalRewards.Set(ctx, newVal.GetOperator(), 0, distrtypes.NewValidatorHistoricalRewards(sdk.DecCoins{}, 1))
	app.DistrKeeper.ValidatorCurrentRewards.Set(ctx, newVal.GetOperator(), distrtypes.NewValidatorCurrentRewards(sdk.DecCoins{}, 1))
	app.DistrKeeper.ValidatorAccumulatedCommission.Set(ctx, newVal.GetOperator(), distrtypes.InitialValidatorAccumulatedCommission())
	app.DistrKeeper.ValidatorOutstandingRewards.Set(ctx, newVal.GetOperator(), distrtypes.ValidatorOutstandingRewards{Rewards: sdk.DecCoins{}})

Slashing

We also need to set the validator signing info for the new validator.

  // SLASHING
	//

	// Set validator signing info for our new validator.
	newConsAddr := sdk.ConsAddress(newValAddr.Bytes())
	newValidatorSigningInfo := slashingtypes.ValidatorSigningInfo{
		Address:     newConsAddr.String(),
		StartHeight: app.LastBlockHeight() - 1,
		Tombstoned:  false,
	}
	app.SlashingKeeper.ValidatorSigningInfo.Set(ctx, newConsAddr, newValidatorSigningInfo)

Bank

It is useful to create new accounts for your testing purposes. This avoids the need to have the same key as you may have on mainnet.

  // BANK
	//

	defaultCoins := sdk.NewCoins(sdk.NewInt64Coin("ustake", 1000000000000))

	localMerlinAccounts := []sdk.AccAddress{
		sdk.MustAccAddressFromBech32("cosmos12smx2wdlyttvyzvzg54y2vnqwq2qjateuf7thj"),
		sdk.MustAccAddressFromBech32("cosmos1cyyzpxplxdzkeea7kwsydadg87357qnahakaks"),
		sdk.MustAccAddressFromBech32("cosmos18s5lynnmx37hq4wlrw9gdn68sg2uxp5rgk26vv"),
		sdk.MustAccAddressFromBech32("cosmos1qwexv7c6sm95lwhzn9027vyu2ccneaqad4w8ka"),
		sdk.MustAccAddressFromBech32("cosmos14hcxlnwlqtq75ttaxf674vk6mafspg8xwgnn53"),
		sdk.MustAccAddressFromBech32("cosmos12rr534cer5c0vj53eq4y32lcwguyy7nndt0u2t"),
		sdk.MustAccAddressFromBech32("cosmos1nt33cjd5auzh36syym6azgc8tve0jlvklnq7jq"),
		sdk.MustAccAddressFromBech32("cosmos10qfrpash5g2vk3hppvu45x0g860czur8ff5yx0"),
		sdk.MustAccAddressFromBech32("cosmos1f4tvsdukfwh6s9swrc24gkuz23tp8pd3e9r5fa"),
		sdk.MustAccAddressFromBech32("cosmos1myv43sqgnj5sm4zl98ftl45af9cfzk7nhjxjqh"),
		sdk.MustAccAddressFromBech32("cosmos14gs9zqh8m49yy9kscjqu9h72exyf295afg6kgk"),
		sdk.MustAccAddressFromBech32("cosmos1jllfytsz4dryxhz5tl7u73v29exsf80vz52ucc")}

  // Fund localMerlin accounts
	for _, account := range localMerlinAccounts {
		err := app.BankKeeper.MintCoins(ctx, minttypes.ModuleName, defaultCoins)
		if err != nil {
			tmos.Exit(err.Error())
		}
		err = app.BankKeeper.SendCoinsFromModuleToAccount(ctx, minttypes.ModuleName, account, defaultCoins)
		if err != nil {
			tmos.Exit(err.Error())
		}
	}

Upgrade

If you would like to schedule an upgrade the below can be used.

	// UPGRADE
	//

	if upgradeToTrigger != "" {
		upgradePlan := upgradetypes.Plan{
			Name:   upgradeToTrigger,
			Height: app.LastBlockHeight(),
		}
		err = app.UpgradeKeeper.ScheduleUpgrade(ctx, upgradePlan)
		if err != nil {
			panic(err)
		}
	}

Optional Changes

If you have custom modules that rely on specific state from the above modules and/or you would like to test your custom module, you will need to update the state of your custom module to reflect your needs

Running the Testnet

Before we can run the testnet we must plug everything together.

in root.go, in the initRootCmd function we add:

server.AddCommands(rootCmd, simapp.DefaultNodeHome, newApp, createMerlinAppAndExport)
+server.AddTestnetCreatorCommand(rootCmd, simapp.DefaultNodeHome, newTestnetApp)

Next we will add a newTestnetApp helper function:

// newTestnetApp starts by running the normal newApp method. From there, the app interface returned is modified in order
// for a testnet to be created from the provided app.
func newTestnetApp(logger log.Logger, db cometbftdb.DB, traceStore io.Writer, appOpts servertypes.AppOptions) servertypes.Application {
	// Create an app and type cast to an MerlinApp
	app := newApp(logger, db, traceStore, appOpts)
	simApp, ok := app.(*simapp.SimApp)
	if !ok {
		panic("app created from newApp is not of type simApp")
	}

	newValAddr, ok := appOpts.Get(server.KeyNewValAddr).(bytes.HexBytes)
	if !ok {
		panic("newValAddr is not of type bytes.HexBytes")
	}
	newValPubKey, ok := appOpts.Get(server.KeyUserPubKey).(crypto.PubKey)
	if !ok {
		panic("newValPubKey is not of type crypto.PubKey")
	}
	newOperatorAddress, ok := appOpts.Get(server.KeyNewOpAddr).(string)
	if !ok {
		panic("newOperatorAddress is not of type string")
	}
	upgradeToTrigger, ok := appOpts.Get(server.KeyTriggerTestnetUpgrade).(string)
	if !ok {
		panic("upgradeToTrigger is not of type string")
	}

	// Make modifications to the normal MerlinApp required to run the network locally
	return meriln.InitMerlinAppForTestnet(simApp, newValAddr, newValPubKey, newOperatorAddress, upgradeToTrigger)
}