Hold a group's batch open for its last member and keep both kinds of member in one batch and one plan (issue 977, part C, ADR 0418)

cmd/mesh-controller/batches_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"io"
 	"os"
 	"slices"
@@ -91,15 +92,16 @@ func noGroups(t *testing.T) {
 	t.Cleanup(func() { deliveryGroupOf = was })
 }
 
-// groupsWaiting stubs mesh-delivery's word on groups for a test: each head named is a group with a member of another
-// repository whose pull request is open (novox/elsewhere, ready), so a merge from it waits for the window (ADR 0306
-// decision 2); every other head names no group.
+// groupsWaiting stubs mesh-delivery's word on groups for a test of the merge window's own timing: each head named
+// is one whose group mesh-delivery cannot say, so a merge from it waits for the window (ADR 0306 decision 2) and
+// nothing holds the batch open; every other head names no group. A group with a member still to merge, which holds
+// its batch open however long it takes (ADR 0418 clause 3), is groupStates'.
 func groupsWaiting(t *testing.T, heads ...string) {
 	t.Helper()
 	was := deliveryGroupOf
 	deliveryGroupOf = func(_ context.Context, _ bool, head string) ([]groupMember, bool, error) {
 		if slices.Contains(heads, head) {
-			return []groupMember{{Repository: "novox/elsewhere", State: "ready"}}, true, nil
+			return nil, false, errors.New("the test's mesh-delivery does not say")
 		}
 		return nil, false, nil
 	}
@@ -107,12 +109,12 @@ func groupsWaiting(t *testing.T, heads ...string) {
 }
 
 // everyHeadWaits stubs mesh-delivery's word on groups for a test whose merges each wait for the window as they did
-// before novox/hq ADR 0304: every head is a group with a member of another repository still to merge.
+// before novox/hq ADR 0304: mesh-delivery cannot say any head's group.
 func everyHeadWaits(t *testing.T) {
 	t.Helper()
 	was := deliveryGroupOf
 	deliveryGroupOf = func(context.Context, bool, string) ([]groupMember, bool, error) {
-		return []groupMember{{Repository: "novox/elsewhere", State: "ready"}}, true, nil
+		return nil, false, errors.New("the test's mesh-delivery does not say")
 	}
 	t.Cleanup(func() { deliveryGroupOf = was })
 }