Relate a batch whose moves are not known to every change

The review found that a merge kept without its moves, judged again at
the cut, gave its batch no modules, so it could read as unrelated to a
walk it will build beside. An unknown change is never unrelated.

cmd/mesh-controller/related_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"strings"
 	"testing"
 
 	"github.com/novox/mesh-controller/internal/inventory"
@@ -90,3 +91,20 @@ func TestFootprintOfBatchWidensToDependents(t *testing.T) {
 		t.Errorf("footprint = %+v; want base-image and nzbget, no head", f)
 	}
 }
+
+// A batch holding a merge kept with no moves (one owed a later look, judged again at the cut) is related to
+// every change, in both orders: what it will move is not known, and an unknown change is never unrelated
+// (issue 525 review).
+func TestABatchWhoseMovesAreNotKnownIsRelatedToEverything(t *testing.T) {
+	unknown := footprintOfBatch([]inventory.BatchedMerge{heardMerge("novox/one", "fix/a", "app"), heardMerge("novox/two", "fix/b")}, nil)
+	other := footprintOfWalk(walkOf("novox/three", "nzbget"), nil)
+	for _, pair := range [][2]footprint{{unknown, other}, {other, unknown}} {
+		if ok, why := related(pair[0], pair[1], nil); !ok || !strings.Contains(why, "not known") {
+			t.Fatalf("an unknown batch read as %v (%q)", ok, why)
+		}
+	}
+	known := footprintOfBatch([]inventory.BatchedMerge{heardMerge("novox/one", "fix/a", "app")}, nil)
+	if ok, why := related(known, other, nil); ok {
+		t.Fatalf("a known, unrelated batch read as related: %q", why)
+	}
+}