Wait for a held node without pinning a pool connection, and give up after a bounded wait naming it (hq ADR 0100)

internal/inventory/hold_test.go

@@ -1,6 +1,8 @@
 package inventory
 
 import (
+	"errors"
+	"strings"
 	"testing"
 	"time"
 )
@@ -42,3 +44,45 @@ func TestHoldingANodeMakesTheNextHolderWait(t *testing.T) {
 		t.Fatal("releasing the node did not let the next holder in")
 	}
 }
+
+// A waiter pins no pool connection while it waits, and gives up after a bounded wait saying which
+// node is busy.
+func TestAWaiterPinsNoConnectionAndGivesUp(t *testing.T) {
+	inv := fresh(t)
+	ctx := t.Context()
+	release, err := inv.HoldNodes(ctx, []string{"anchor"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer release()
+	savedWait, savedPoll := HoldWaitFor, HoldPoll
+	HoldWaitFor, HoldPoll = 1500*time.Millisecond, 50*time.Millisecond
+	defer func() { HoldWaitFor, HoldPoll = savedWait, savedPoll }()
+
+	pool := inv.store.Pool()
+	base := pool.Stat().AcquiredConns()
+	const waiters = 3
+	done := make(chan error, waiters)
+	for range waiters {
+		go func() {
+			_, err := inv.HoldNodes(ctx, []string{"anchor"})
+			done <- err
+		}()
+	}
+	// While they wait, the pool lends nothing to them for longer than a look.
+	pinned := 0
+	for range 10 {
+		time.Sleep(60 * time.Millisecond)
+		if n := int(pool.Stat().AcquiredConns() - base); n > pinned {
+			pinned = n
+		}
+	}
+	if pinned >= waiters {
+		t.Fatalf("%d connections were held by %d waiters", pinned, waiters)
+	}
+	for range waiters {
+		if err := <-done; !errors.Is(err, ErrNodeBusy) || !strings.Contains(err.Error(), "anchor") {
+			t.Fatalf("a waiter did not give up naming the busy node: %v", err)
+		}
+	}
+}