Hold a node from composing to sending, so a push composed before converge or adopt is never sent after it (hq ADR 0100)

internal/inventory/hold_test.go

@@ -0,0 +1,44 @@
+package inventory
+
+import (
+	"testing"
+	"time"
+)
+
+// Composing and sending one node's declaration is serialised: a second holder waits for the first.
+func TestHoldingANodeMakesTheNextHolderWait(t *testing.T) {
+	inv := fresh(t)
+	ctx := t.Context()
+	release, err := inv.HoldNodes(ctx, []string{"anchor", "laptop"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := make(chan func(), 1)
+	go func() {
+		second, err := inv.HoldNodes(ctx, []string{"laptop"})
+		if err != nil {
+			t.Error(err)
+			got <- func() {}
+			return
+		}
+		got <- second
+	}()
+	select {
+	case <-got:
+		t.Fatal("a node held by one caller was held by another at the same time")
+	case <-time.After(300 * time.Millisecond):
+	}
+	// Another node is not held up.
+	other, err := inv.HoldNodes(ctx, []string{"joiner"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	other()
+	release()
+	select {
+	case second := <-got:
+		second()
+	case <-time.After(5 * time.Second):
+		t.Fatal("releasing the node did not let the next holder in")
+	}
+}