test(gov): Refactor x/gov keeper tests to use mocks (#12988)

## Description

ref: #12752 

- [x] Move some keeper tests into `tests/integration/gov/keeper`, see https://github.com/cosmos/cosmos-sdk/pull/12988#discussion_r954956199
- [x] Don't use simapp in `x/gov/keeper` tests, use mocks instead
- [x] Find 0 "simapp" occurence in x/gov/keeper. (Note: other occurrences of simapp are removed in  #13043)



---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] 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
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#pr-targeting))
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- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/main/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/main/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
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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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)

testutil/sims/address_helpers.go

@@ -13,13 +13,19 @@ import (
 	"github.com/cosmos/cosmos-sdk/types/errors"
 	bankkeeper "github.com/cosmos/cosmos-sdk/x/bank/keeper"
 	minttypes "github.com/cosmos/cosmos-sdk/x/mint/types"
-	stakingkeeper "github.com/cosmos/cosmos-sdk/x/staking/keeper"
 )
 
 type GenerateAccountStrategy func(int) []sdk.AccAddress
 
+// BondDenomProvider is a subset of the staking keeper's public interface that
+// provides the staking bond denom. It is used in arguments in this package's
+// functions so that a mock staking keeper can be passed instead of the real one.
+type BondDenomProvider interface {
+	BondDenom(ctx sdk.Context) string
+}
+
 // AddTestAddrsFromPubKeys adds the addresses into the SimApp providing only the public keys.
-func AddTestAddrsFromPubKeys(bankKeeper bankkeeper.Keeper, stakingKeeper *stakingkeeper.Keeper, ctx sdk.Context, pubKeys []cryptotypes.PubKey, accAmt math.Int) {
+func AddTestAddrsFromPubKeys(bankKeeper bankkeeper.Keeper, stakingKeeper BondDenomProvider, ctx sdk.Context, pubKeys []cryptotypes.PubKey, accAmt math.Int) {
 	initCoins := sdk.NewCoins(sdk.NewCoin(stakingKeeper.BondDenom(ctx), accAmt))
 
 	for _, pk := range pubKeys {
@@ -29,16 +35,16 @@ func AddTestAddrsFromPubKeys(bankKeeper bankkeeper.Keeper, stakingKeeper *stakin
 
 // AddTestAddrs constructs and returns accNum amount of accounts with an
 // initial balance of accAmt in random order
-func AddTestAddrs(bankKeeper bankkeeper.Keeper, stakingKeeper *stakingkeeper.Keeper, ctx sdk.Context, accNum int, accAmt math.Int) []sdk.AccAddress {
+func AddTestAddrs(bankKeeper bankkeeper.Keeper, stakingKeeper BondDenomProvider, ctx sdk.Context, accNum int, accAmt math.Int) []sdk.AccAddress {
 	return addTestAddrs(bankKeeper, stakingKeeper, ctx, accNum, accAmt, CreateRandomAccounts)
 }
 
 // AddTestAddrsIncremental constructs and returns accNum amount of accounts with an initial balance of accAmt in random order
-func AddTestAddrsIncremental(bankKeeper bankkeeper.Keeper, stakingKeeper *stakingkeeper.Keeper, ctx sdk.Context, accNum int, accAmt math.Int) []sdk.AccAddress {
+func AddTestAddrsIncremental(bankKeeper bankkeeper.Keeper, stakingKeeper BondDenomProvider, ctx sdk.Context, accNum int, accAmt math.Int) []sdk.AccAddress {
 	return addTestAddrs(bankKeeper, stakingKeeper, ctx, accNum, accAmt, CreateIncrementalAccounts)
 }
 
-func addTestAddrs(bankKeeper bankkeeper.Keeper, stakingKeeper *stakingkeeper.Keeper, ctx sdk.Context, accNum int, accAmt math.Int, strategy GenerateAccountStrategy) []sdk.AccAddress {
+func addTestAddrs(bankKeeper bankkeeper.Keeper, stakingKeeper BondDenomProvider, ctx sdk.Context, accNum int, accAmt math.Int, strategy GenerateAccountStrategy) []sdk.AccAddress {
 	testAddrs := strategy(accNum)
 	initCoins := sdk.NewCoins(sdk.NewCoin(stakingKeeper.BondDenom(ctx), accAmt))