Test that the composition marks a need its provider's helper answers, so the consumer's plan keys it (issue 774)

The review found answeredByHelper untested: forced false, every test passed. This row fails then.

go/compose/resolve_test.go

@@ -358,3 +358,31 @@ func TestALicenceKeyTheInputDoesNotCarryIsAStandInAndNamedForeseen(t *testing.T)
 		t.Errorf("a key the mesh holds none of: %q %v", n.Sealed, got.Foreseen)
 	}
 }
+
+// A consumer not handed of a provision whose provider's offer says the helper answers it has that provision in a plan of
+// its own (issue 774: grafana's route): the composition marks the need answered by the helper, and the plan keys it.
+func TestANeedAnsweredByTheHelperIsInTheConsumersPlan(t *testing.T) {
+	in := theStoreMesh(t)
+	store := in.Catalogue["store"]
+	store.Provides = []catalogue.Offer{{Name: "postgres-database", Scope: catalogue.ScopeMesh, AnsweredBy: catalogue.AnsweredByHelper}}
+	in.Catalogue["store"] = store
+	got, err := Resolve(in, "laptop")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n := need(t, got.Plan, "board", "postgres-database"); !n.AnsweredByHelper {
+		t.Fatalf("the need is not marked answered by the helper: %+v", n)
+	}
+	with := rendered(t, in, "laptop", Foreseeing).Rendering
+	with.Hands, with.Provisioner = true, "mesh-provisioner-client"
+	if with.Generators, err = newComposer(in).generators(); err != nil {
+		t.Fatal(err)
+	}
+	c, err := got.Plan.Compose(with)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if p := c.Plans["board"].Provisions; len(p) != 1 || p[0].Provision != "postgres-database" || p[0].ProviderModule != "store" {
+		t.Fatalf("board's plan is %+v", c.Plans["board"])
+	}
+}