x/mint/simulation/genesis.go: add unit tests (#6706)

* x/mint/simulation/gemesis.go: add unit tests

* Rename file

Co-authored-by: Alessio Treglia <alessio@tendermint.com>
Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

x/mint/simulation/genesis_test.go

@@ -0,0 +1,83 @@
+package simulation_test
+
+import (
+	"encoding/json"
+	"math/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/cosmos/cosmos-sdk/codec"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/types/module"
+	simtypes "github.com/cosmos/cosmos-sdk/types/simulation"
+	"github.com/cosmos/cosmos-sdk/x/mint/simulation"
+	"github.com/cosmos/cosmos-sdk/x/mint/types"
+)
+
+// TestRandomizedGenState tests the normal scenario of applying RandomizedGenState.
+// Abonormal scenarios are not tested here.
+func TestRandomizedGenState(t *testing.T) {
+	cdc := codec.New()
+	s := rand.NewSource(1)
+	r := rand.New(s)
+
+	simState := module.SimulationState{
+		AppParams:    make(simtypes.AppParams),
+		Cdc:          cdc,
+		Rand:         r,
+		NumBonded:    3,
+		Accounts:     simtypes.RandomAccounts(r, 3),
+		InitialStake: 1000,
+		GenState:     make(map[string]json.RawMessage),
+	}
+
+	simulation.RandomizedGenState(&simState)
+
+	var mintGenesis types.GenesisState
+	simState.Cdc.MustUnmarshalJSON(simState.GenState[types.ModuleName], &mintGenesis)
+
+	dec1, _ := sdk.NewDecFromStr("0.670000000000000000")
+	dec2, _ := sdk.NewDecFromStr("0.200000000000000000")
+	dec3, _ := sdk.NewDecFromStr("0.070000000000000000")
+
+	require.Equal(t, uint64(6311520), mintGenesis.Params.BlocksPerYear)
+	require.Equal(t, dec1, mintGenesis.Params.GoalBonded)
+	require.Equal(t, dec2, mintGenesis.Params.InflationMax)
+	require.Equal(t, dec3, mintGenesis.Params.InflationMin)
+	require.Equal(t, "stake", mintGenesis.Params.MintDenom)
+
+	require.Equal(t, dec3, mintGenesis.Params.InflationMin)
+
+	require.Equal(t, "0stake", mintGenesis.Minter.BlockProvision(mintGenesis.Params).String())
+	require.Equal(t, "0.170000000000000000", mintGenesis.Minter.NextAnnualProvisions(mintGenesis.Params, sdk.OneInt()).String())
+	require.Equal(t, "0.169999926644441493", mintGenesis.Minter.NextInflationRate(mintGenesis.Params, sdk.OneDec()).String())
+	require.Equal(t, "0.170000000000000000", mintGenesis.Minter.Inflation.String())
+	require.Equal(t, "0.000000000000000000", mintGenesis.Minter.AnnualProvisions.String())
+}
+
+// TestRandomizedGenState tests abnormal scenarios of applying RandomizedGenState.
+func TestRandomizedGenState1(t *testing.T) {
+	cdc := codec.New()
+
+	s := rand.NewSource(1)
+	r := rand.New(s)
+	// all these tests will panic
+	tests := []struct {
+		simState module.SimulationState
+		panicMsg string
+	}{
+		{ // panic => reason: incomplete initialization of the simState
+			module.SimulationState{}, "invalid memory address or nil pointer dereference"},
+		{ // panic => reason: incomplete initialization of the simState
+			module.SimulationState{
+				AppParams: make(simtypes.AppParams),
+				Cdc:       cdc,
+				Rand:      r,
+			}, "assignment to entry in nil map"},
+	}
+
+	for _, tt := range tests {
+		require.Panicsf(t, func() { simulation.RandomizedGenState(&tt.simState) }, tt.panicMsg)
+	}
+}