[#76] Add UNIQUE keyword

Signed-off-by: Alejandro Lopez <a.lopez@yadro.com>

netmap/selector_test.go

@@ -1,6 +1,7 @@
 package netmap
 
 import (
+	"encoding/binary"
 	"fmt"
 	"math/rand"
 	"sort"
@@ -244,6 +245,43 @@ func TestPlacementPolicy_ProcessSelectors(t *testing.T) {
 	}
 }
 
+func TestPlacementPolicy_Unique(t *testing.T) {
+	p := newPlacementPolicy(2,
+		[]ReplicaDescriptor{
+			newReplica(1, "S"),
+			newReplica(1, "S"),
+		},
+		[]Selector{
+			newSelector("S", "City", 1, "*", (*Selector).SelectSame),
+		},
+		[]Filter{})
+	p.unique = true
+
+	var nodes []NodeInfo
+	for i, city := range []string{"Moscow", "Berlin", "Shenzhen"} {
+		for j := 0; j < 3; j++ {
+			node := nodeInfoFromAttributes("City", city)
+			node.SetPublicKey(binary.BigEndian.AppendUint16(nil, uint16(i*4+j)))
+			nodes = append(nodes, node)
+		}
+	}
+
+	var nm NetMap
+	nm.SetNodes(nodes)
+
+	v, err := nm.ContainerNodes(p, nil)
+	require.NoError(t, err)
+	for i, vi := range v {
+		for _, ni := range vi {
+			for j := 0; j < i; j++ {
+				for _, nj := range v[j] {
+					require.NotEqual(t, ni.hash, nj.hash)
+				}
+			}
+		}
+	}
+}
+
 func TestPlacementPolicy_ProcessSelectorsExceptForNodes(t *testing.T) {
 	p := newPlacementPolicy(1, nil,
 		[]Selector{