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Chain simulation

The Ignite CLI chain simulator can help you to run your chain based in randomized inputs for you can make fuzz testing and also benchmark test for your chain, simulating the messages, blocks, and accounts. You can scaffold a template to perform simulation testing in each module along with a boilerplate simulation methods for each scaffolded message.

Module simulation

Every new module that is scaffolded with Ignite CLI implements the Cosmos SDK Module Simulation.

  • Each new message creates a file with the simulation methods required for the tests.
  • Scaffolding a CRUD type like a list or map creates a simulation file with create, update, and delete simulation methods in the x/<module>/simulation folder and registers these methods in x/<module>/module_simulation.go.
  • Scaffolding a single message creates an empty simulation method to be implemented by the user.

We recommend that you maintain the simulation methods for each new modification into the message keeper methods.

Every simulation is weighted because the sender of the operation is assigned randomly. The weight defines how much the simulation calls the message.

For better randomizations, you can define a random seed. The simulation with the same random seed is deterministic with the same output.

Scaffold a simulation

To create a new chain:

ignite scaffold chain mars

Review the empty x/mars/simulation folder and the x/mars/module_simulation.go file to see that a simulation is not registered.

Now, scaffold a new message:

ignite scaffold list user address balance:uint state

A new file x/mars/simulation/user.go is created and is registered with the weight in the x/mars/module_simulation.go file.

Be sure to define the proper simulation weight with a minimum weight of 0 and a maximum weight of 100.

For this example, change the defaultWeightMsgDeleteUser to 30 and the defaultWeightMsgUpdateUser to 50.

Run the BenchmarkSimulation method into app/simulation_test.go to run simulation tests for all modules:

ignite chain simulate

You can also define flags that are provided by the simulation. Flags are defined by the method simapp.GetSimulatorFlags():

ignite chain simulate -v --numBlocks 200 --blockSize 50 --seed 33

Wait for the entire simulation to finish and check the result of the messages.

The default go test command works to run the simulation:

go test -v -benchmem -run=^$ -bench ^BenchmarkSimulation -cpuprofile cpu.out ./app -Commit=true

Skip message

Use logic to avoid sending a message without returning an error. Return only simtypes.NoOpMsg(...) into the simulation message handler.


Scaffolding a module with params automatically adds the module in the module_simulaton.go file:

ignite s module earth --params channel:string,minLaunch:uint,maxLaunch:int

After the parameters are scaffolded, change the x/<module>/module_simulation.go file to set the random parameters into the RandomizedParams method. The simulation will change the params randomly according to call the function.


Simulating a chain can help you prevent chain invariants errors. An invariant is a function called by the chain to check if something broke, invalidating the chain data. To create a new invariant and check the chain integrity, you must create a method to validate the invariants and register all invariants.

For example, in x/earth/keeper/invariants.go:

package keeper

import (

sdk ""

const zeroLaunchTimestampRoute = "zero-launch-timestamp"

// RegisterInvariants registers all module invariants
func RegisterInvariants(ir sdk.InvariantRegistry, k Keeper) {
ir.RegisterRoute(types.ModuleName, zeroLaunchTimestampRoute,

// ZeroLaunchTimestampInvariant invariant that checks if the
// `LaunchTimestamp is zero
func ZeroLaunchTimestampInvariant(k Keeper) sdk.Invariant {
return func(ctx sdk.Context) (string, bool) {
all := k.GetAllChain(ctx)
for _, chain := range all {
if chain.LaunchTimestamp == 0 {
return sdk.FormatInvariant(
types.ModuleName, zeroLaunchTimestampRoute,
"LaunchTimestamp is not set while LaunchTriggered is set",
), true
return "", false

Now, register the keeper invariants into the x/earth/module.go file:

// RegisterInvariants registers the capability module's invariants.
func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
keeper.RegisterInvariants(ir, am.keeper)