tabletbalancer test coverage for tablet replaced

Signed-off-by: Venkatraju V <venkatraju@slack-corp.com>

go/vt/vtgate/balancer/balancer_test.go

@@ -384,4 +384,26 @@ func TestTopologyChanged(t *testing.T) {
  t.Errorf("shuffle promoted wrong tablet from cell %s", allTablets[0].Tablet.Alias.Cell)
  }
  }
+
+ // Run again with a node in the topology replaced.
+ newTablet := createTestTablet("b")
+ allTablets[2] = newTablet
+ for i := 0; i < N; i++ {
+ th := b.Pick(target, allTablets)
+
+ allocation, totalAllocation := b.getAllocation(target, allTablets)
+
+ if totalAllocation != ALLOCATION/2 {
+ t.Errorf("totalAllocation mismatch %s", b.print())
+ }
+
+ if allocation[th.Tablet.Alias.Uid] != ALLOCATION/4 {
+ t.Errorf("allocation mismatch %s, cell %s", b.print(), allTablets[0].Tablet.Alias.Cell)
+ }
+
+ if th.Tablet.Alias.Cell != "b" {
+ t.Errorf("shuffle promoted wrong tablet from cell %s", allTablets[0].Tablet.Alias.Cell)
+ }
+ }
+
 }