Add test for adding new collector after completed initial allocation

cmd/otel-allocator/allocation/allocatortest.go

@@ -35,9 +35,8 @@ func MakeNNewTargets(n int, numCollectors int, startingIndex int) map[string]*ta
 	for i := startingIndex; i < n+startingIndex; i++ {
 		collector := fmt.Sprintf("collector-%d", colIndex(i, numCollectors))
 		label := model.LabelSet{
-			"collector": model.LabelValue(collector),
-			"i":         model.LabelValue(strconv.Itoa(i)),
-			"total":     model.LabelValue(strconv.Itoa(n + startingIndex)),
+			"i":     model.LabelValue(strconv.Itoa(i)),
+			"total": model.LabelValue(strconv.Itoa(n + startingIndex)),
 		}
 		newTarget := target.NewItem(fmt.Sprintf("test-job-%d", i), fmt.Sprintf("test-url-%d", i), label, collector)
 		toReturn[newTarget.Hash()] = newTarget

cmd/otel-allocator/allocation/least_weighted_test.go

@@ -15,6 +15,7 @@
 package allocation
 
 import (
+	"fmt"
 	"math"
 	"math/rand"
 	"testing"
@@ -144,6 +145,56 @@ func TestNoCollectorReassignment(t *testing.T) {
 
 }
 
+// Tests that the newly added collector instance does not get assigned any target when the targets remain the same.
+func TestNoAssignmentToNewCollector(t *testing.T) {
+	s, _ := New("least-weighted", logger)
+
+	// instantiate only 1 collector
+	cols := MakeNCollectors(1, 0)
+	s.SetCollectors(cols)
+
+	expectedColLen := len(cols)
+	assert.Len(t, s.Collectors(), expectedColLen)
+
+	for _, i := range cols {
+		assert.NotNil(t, s.Collectors()[i.Name])
+	}
+
+	initialColsBeforeAddingNewCol := s.Collectors()
+	initTargets := MakeNNewTargets(6, 0, 0)
+
+	// test that targets and collectors are added properly
+	s.SetTargets(initTargets)
+
+	// verify
+	expectedTargetLen := len(initTargets)
+	targetItems := s.TargetItems()
+	assert.Len(t, targetItems, expectedTargetLen)
+
+	// add another collector
+	newColName := fmt.Sprintf("collector-%d", len(cols))
+	cols[newColName] = &Collector{
+		Name:       newColName,
+		NumTargets: 0,
+	}
+	s.SetCollectors(cols)
+
+	// targets shall not change
+	newTargetItems := s.TargetItems()
+	assert.Equal(t, targetItems, newTargetItems)
+
+	// initial collectors still should have the same targets
+	for colName, col := range s.Collectors() {
+		if colName != newColName {
+			assert.Equal(t, initialColsBeforeAddingNewCol[colName], col)
+		}
+	}
+
+	// new collector should have no targets
+	newCollector := s.Collectors()[newColName]
+	assert.Equal(t, newCollector.NumTargets, 0)
+}
+
 func TestSmartCollectorReassignment(t *testing.T) {
 	t.Skip("This test is flaky and fails frequently, see issue 1291")
 	s, _ := New("least-weighted", logger)