feat: Add simulations to group module (#10723)

## Description

Closes: #9901



---

### 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
- [ ] 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
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [x] 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`
- [x] 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
- [x] 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)

x/group/module/module.go

@@ -19,7 +19,8 @@ import (
 	simtypes "github.com/cosmos/cosmos-sdk/types/simulation"
 	"github.com/cosmos/cosmos-sdk/x/group"
 	"github.com/cosmos/cosmos-sdk/x/group/client/cli"
-	groupkeeper "github.com/cosmos/cosmos-sdk/x/group/keeper"
+	"github.com/cosmos/cosmos-sdk/x/group/keeper"
+	"github.com/cosmos/cosmos-sdk/x/group/simulation"
 )
 
 var (
@@ -30,19 +31,19 @@ var (
 
 type AppModule struct {
 	AppModuleBasic
-	keeper        groupkeeper.Keeper
-	BankKeeper    group.BankKeeper
-	AccountKeeper group.AccountKeeper
-	registry      cdctypes.InterfaceRegistry
+	keeper     keeper.Keeper
+	bankKeeper group.BankKeeper
+	accKeeper  group.AccountKeeper
+	registry   cdctypes.InterfaceRegistry
 }
 
 // NewAppModule creates a new AppModule object
-func NewAppModule(cdc codec.Codec, keeper groupkeeper.Keeper, ak group.AccountKeeper, bk group.BankKeeper, registry cdctypes.InterfaceRegistry) AppModule {
+func NewAppModule(cdc codec.Codec, keeper keeper.Keeper, ak group.AccountKeeper, bk group.BankKeeper, registry cdctypes.InterfaceRegistry) AppModule {
 	return AppModule{
 		AppModuleBasic: AppModuleBasic{cdc: cdc},
 		keeper:         keeper,
-		BankKeeper:     bk,
-		AccountKeeper:  ak,
+		bankKeeper:     bk,
+		accKeeper:      ak,
 		registry:       registry,
 	}
 }
@@ -107,7 +108,7 @@ func (AppModule) Name() string {
 
 // RegisterInvariants does nothing, there are no invariants to enforce
 func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
-	groupkeeper.RegisterInvariants(ir, am.keeper)
+	keeper.RegisterInvariants(ir, am.keeper)
 }
 
 // Deprecated: Route returns the message routing key for the group module.
@@ -164,6 +165,7 @@ func (am AppModule) EndBlock(ctx sdk.Context, _ abci.RequestEndBlock) []abci.Val
 
 // GenerateGenesisState creates a randomized GenState of the group module.
 func (AppModule) GenerateGenesisState(simState *module.SimulationState) {
+	simulation.RandomizedGenState(simState)
 }
 
 // ProposalContents returns all the group content functions used to
@@ -179,10 +181,13 @@ func (AppModule) RandomizedParams(r *rand.Rand) []simtypes.ParamChange {
 
 // RegisterStoreDecoder registers a decoder for group module's types
 func (am AppModule) RegisterStoreDecoder(sdr sdk.StoreDecoderRegistry) {
+	sdr[group.StoreKey] = simulation.NewDecodeStore(am.cdc)
 }
 
 // WeightedOperations returns the all the gov module operations with their respective weights.
 func (am AppModule) WeightedOperations(simState module.SimulationState) []simtypes.WeightedOperation {
-	// TODO
-	return nil
+	return simulation.WeightedOperations(
+		simState.AppParams, simState.Cdc,
+		am.accKeeper, am.bankKeeper, am.keeper, am.cdc,
+	)
 }