Keep the started walk started in the let-go test by holding its key, since a walk takes keys at once now (issue 1931)

cmd/mesh-controller/away_integration_test.go

@@ -78,7 +78,7 @@ func TestAPlanGoesOnWithoutAMachineAwayWhenItsTierIsSent(t *testing.T) {
 	holdB.Store(true)
 	openPlanKeys = func() (planKeyReads, func(), error) {
 		all, done, err := wholeKeys()
-		return keysHolding{all, "b", &holdB}, done, err
+		return keysHolding{all, "b", &holdB, ""}, done, err
 	}
 	digests := 0
 	wasSend := sendRollout
@@ -226,15 +226,17 @@ func TestAPlanGoesOnWithoutAMachineAwayWhenItsTierIsSent(t *testing.T) {
 	}
 }
 
-// keysHolding is the stand-in builder's keys but for one module, whose key is not built while held.
+// keysHolding is the stand-in builder's keys but for one module, whose key is not built while held; only the key of
+// the fingerprint fp when that is given.
 type keysHolding struct {
 	planKeyReads
 	module string
 	held   *atomic.Bool
+	fp     string
 }
 
 func (k keysHolding) Build(ctx context.Context, module, fp string) (builderkeys.Key, error) {
-	if module == k.module && k.held.Load() {
+	if module == k.module && k.held.Load() && (k.fp == "" || fp == k.fp) {
 		return builderkeys.Key{Module: module, Fingerprint: fp}, nil
 	}
 	return k.planKeyReads.Build(ctx, module, fp)

cmd/mesh-controller/batches_integration_test.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 	"slices"
+	"sync/atomic"
 	"strings"
 	"testing"
 	"time"
@@ -512,6 +513,14 @@ func TestALateMergeOfAOneModuleRepositoryIsNamed(t *testing.T) {
 func TestAWalkLetGoBesideAStartedOneStartsOnceItEnded(t *testing.T) {
 	open := windowed(t)
 	asked := asksWithPaths(t)
+	// The started walk's key (one at c1) is not built, so that walk stays started as it did while its build ran: with
+	// the stand-in builder's key done at once, one step would carry it to done and nothing would be beside the other.
+	wholeKeys, held := openPlanKeys, &atomic.Bool{}
+	held.Store(true)
+	openPlanKeys = func() (planKeyReads, func(), error) {
+		all, done, err := wholeKeys()
+		return keysHolding{all, "one", held, fpOfModuleAt("one", "c1")}, done, err
+	}
 	ctx := t.Context()
 	hear(t, open, repoMerge("one", "c1", t0), t0)
 	cutAt(t, open, t0.Add(2*time.Minute))