lint: errcheck (#5091)

## Description

add more error checks to tests


gonna do a third PR that tackles the non test cases

blockchain/v0/pool_test.go

@@ -90,7 +90,11 @@ func TestBlockPoolBasic(t *testing.T) {
 		t.Error(err)
 	}
 
-	defer pool.Stop()
+	t.Cleanup(func() {
+		if err := pool.Stop(); err != nil {
+			t.Error(err)
+		}
+	})
 
 	peers.start()
 	defer peers.stop()
@@ -144,7 +148,11 @@ func TestBlockPoolTimeout(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	defer pool.Stop()
+	t.Cleanup(func() {
+		if err := pool.Stop(); err != nil {
+			t.Error(err)
+		}
+	})
 
 	for _, peer := range peers {
 		t.Logf("Peer %v", peer.id)
@@ -206,7 +214,11 @@ func TestBlockPoolRemovePeer(t *testing.T) {
 	pool.SetLogger(log.TestingLogger())
 	err := pool.Start()
 	require.NoError(t, err)
-	defer pool.Stop()
+	t.Cleanup(func() {
+		if err := pool.Stop(); err != nil {
+			t.Error(err)
+		}
+	})
 
 	// add peers
 	for peerID, peer := range peers {

blockchain/v2/reactor_test.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	dbm "github.com/tendermint/tm-db"
 
 	abci "github.com/tendermint/tendermint/abci/types"
@@ -387,7 +388,8 @@ func TestReactorHelperMode(t *testing.T) {
 			reactor := newTestReactor(params)
 			mockSwitch := &mockSwitchIo{switchedToConsensus: false}
 			reactor.io = mockSwitch
-			reactor.Start()
+			err := reactor.Start()
+			require.NoError(t, err)
 
 			for i := 0; i < len(tt.msgs); i++ {
 				step := tt.msgs[i]
@@ -415,7 +417,8 @@ func TestReactorHelperMode(t *testing.T) {
 					}
 				}
 			}
-			reactor.Stop()
+			err = reactor.Stop()
+			require.NoError(t, err)
 		})
 	}
 }