[#326] pool: Add test for concurrent client deletion

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

pool/tree/pool_test.go

@@ -10,6 +10,7 @@ import (
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
 	cidtest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id/test"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap"
+	netmaptest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/netmap/test"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/pool"
 	"git.frostfs.info/TrueCloudLab/hrw"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
@@ -416,6 +417,21 @@ func TestRetryContainerNodes(t *testing.T) {
 	})
 }
 
+func TestDeleteClientTwice(t *testing.T) {
+	p := Pool{
+		clientMap: makeClientMap([]netmap.NodeInfo{netmaptest.NodeInfo()}),
+	}
+	// emulate concurrent requests as consecutive requests
+	// to delete the same client from the map twice
+	for idToDelete := range p.clientMap {
+		p.deleteClientFromMap(idToDelete)
+		require.NotPanics(t, func() {
+			p.deleteClientFromMap(idToDelete)
+		})
+	}
+	require.Empty(t, p.clientMap)
+}
+
 func makeInnerPool(nodes [][]string) []*innerPool {
 	res := make([]*innerPool, len(nodes))