WIP

cluster2/src/main/java/io/scalecube/cluster2/gossip/GossipProtocol.java

@@ -304,11 +304,18 @@ void nextGossipMembers() {
 
       final int step = gossipFanout;
       final int limit = step * (size / step);
-      final int nextLimit = index + step;
+      final int nextLimit;
 
-      if (nextLimit > limit) {
+      if (index >= limit) {
         index = 0;
+        nextLimit = step;
         shuffle();
+      } else {
+        nextLimit = index + step;
+        if (nextLimit > limit) {
+          index = 0;
+          shuffle();
+        }
       }
 
       for (; index < nextLimit; index++) {

cluster2/src/test/java/io/scalecube/cluster2/gossip/MemberSelectorTest.java

@@ -0,0 +1,88 @@
+package io.scalecube.cluster2.gossip;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasItems;
+import static org.hamcrest.Matchers.isOneOf;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.scalecube.cluster2.Member;
+import io.scalecube.cluster2.gossip.GossipProtocol.MemberSelector;
+import java.util.ArrayList;
+import java.util.UUID;
+import org.junit.jupiter.api.Test;
+
+@SuppressWarnings("unchecked")
+public class MemberSelectorTest {
+
+  private final Member fooMember = new Member(UUID.randomUUID(), "foo:1");
+  private final Member barMember = new Member(UUID.randomUUID(), "bar:2");
+  private final Member bazMember = new Member(UUID.randomUUID(), "baz:3");
+  private final Member aliceMember = new Member(UUID.randomUUID(), "alice:4");
+  private final Member bobMember = new Member(UUID.randomUUID(), "bob:5");
+  private final Member johnMember = new Member(UUID.randomUUID(), "john:6");
+  private final Member eveMember = new Member(UUID.randomUUID(), "eve:7");
+  private final Member abcMember = new Member(UUID.randomUUID(), "abc:8");
+  private final Member xyzMember = new Member(UUID.randomUUID(), "abc:9");
+
+  private final ArrayList<Member> remoteMembers = new ArrayList<>();
+  private final ArrayList<Member> gossipMembers = new ArrayList<>();
+
+  @Test
+  void testSelectNothing() {
+    final MemberSelector memberSelector = new MemberSelector(3, remoteMembers, gossipMembers);
+    memberSelector.nextGossipMembers();
+    assertEquals(0, gossipMembers.size());
+  }
+
+  @Test
+  void testSelectWhenLessThanFanout() {
+    remoteMembers.add(fooMember);
+    remoteMembers.add(barMember);
+    remoteMembers.add(bazMember);
+
+    final MemberSelector memberSelector = new MemberSelector(5, remoteMembers, gossipMembers);
+
+    for (int i = 0; i < 10; i++) {
+      memberSelector.nextGossipMembers();
+      assertEquals(3, gossipMembers.size());
+      assertThat(gossipMembers, hasItems(isOneOf(fooMember, barMember, bazMember)));
+    }
+  }
+
+  @Test
+  void testSelectWhenEqualToFanout() {
+    remoteMembers.add(fooMember);
+    remoteMembers.add(barMember);
+    remoteMembers.add(bazMember);
+
+    final MemberSelector memberSelector = new MemberSelector(3, remoteMembers, gossipMembers);
+
+    for (int i = 0; i < 10; i++) {
+      memberSelector.nextGossipMembers();
+      assertEquals(3, gossipMembers.size());
+      assertThat(gossipMembers, hasItems(isOneOf(fooMember, barMember, bazMember)));
+    }
+  }
+
+  @Test
+  void testSelectWhenGreaterThanFanout() {
+    remoteMembers.add(fooMember);
+    remoteMembers.add(barMember);
+    remoteMembers.add(bazMember);
+    remoteMembers.add(aliceMember);
+    remoteMembers.add(bobMember);
+    remoteMembers.add(johnMember);
+    remoteMembers.add(eveMember);
+    remoteMembers.add(abcMember);
+    remoteMembers.add(xyzMember);
+
+    final MemberSelector memberSelector = new MemberSelector(3, remoteMembers, gossipMembers);
+
+    for (int i = 0; i < 10; i++) {
+      memberSelector.nextGossipMembers();
+      assertEquals(3, gossipMembers.size());
+      System.err.println(gossipMembers);
+      // assertThat(gossipMembers, hasItems(isOneOf(fooMember, barMember, bazMember)));
+    }
+  }
+}