Apply suggestions from code review

Co-authored-by: Michael Schurter <mschurter@hashicorp.com>

scheduler/spread_test.go

@@ -636,7 +636,8 @@ func TestSpreadOnLargeCluster(t *testing.T) {
 		},
 	}
 
-	for _, tc := range cases {
+	for i := range cases {
+		tc := cases[i]
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 			h := NewHarness(t)
@@ -765,6 +766,7 @@ func validateEqualSpread(h *Harness) error {
 	}
 	i := 0
 	nodesToRacks := map[string]string{}
+	racksToAllocCount := map[string]int{}
 	for {
 		raw := iter.Next()
 		if raw == nil {
@@ -774,14 +776,14 @@ func validateEqualSpread(h *Harness) error {
 		rack, ok := node.Meta["rack"]
 		if ok {
 			nodesToRacks[node.ID] = rack
+			racksToAllocCount[rack] = 0
 		}
 		i++
 	}
 
 	// Collapse the count of allocations per node into a list of
 	// counts. The results should be a single count or, if more than
 	// one count, they should be no more than one apart.
-	racksToAllocCount := map[string]int{}
 	for nodeID, nodeAllocs := range h.Plans[0].NodeAllocation {
 		racksToAllocCount[nodesToRacks[nodeID]] += len(nodeAllocs)
 	}