test(13-06): pin that a family falls through a member whose constraint fails

- TestOverlapConstraintFallsThrough: an earlier member that matches the
  literals but not its Where constraint must let a later member answer;
  the routes.php pairs cannot show this, since each member's own handler
  re-checks its constraints and the pairs differ in their literals (T-13-23)

modules/surf/overlap_edges_test.go

@@ -146,3 +146,27 @@ func TestOverlapUnsupportedShapes(t *testing.T) {
 		})
 	}
 }
+
+// TestOverlapConstraintFallsThrough: when an earlier member matches the
+// literals but not its constraint, the family tries the next member
+// instead of answering for the first one, as Laravel's router walks its
+// routes in order.
+func TestOverlapConstraintFallsThrough(t *testing.T) {
+	h := compileOverlap(t, []overlapRoute{
+		{name: "by-number", method: "GET", path: "/drawers/{id}/open", where: map[string]string{"id": "[0-9]+"}},
+		{name: "by-name", method: "GET", path: "/drawers/top/{action}"},
+	})
+	for _, c := range []struct{ path, want string }{
+		{"/drawers/top/open", "by-name action=open"},
+		{"/drawers/7/open", "by-number id=7"},
+		{"/drawers/top/close", "by-name action=close"},
+	} {
+		rec := serve(h, "GET", c.path)
+		if rec.Code != http.StatusOK || rec.Body.String() != c.want {
+			t.Errorf("GET %s = %d %q, want 200 %q", c.path, rec.Code, rec.Body.String(), c.want)
+		}
+	}
+	if rec := serve(h, "GET", "/drawers/x/open"); rec.Code != http.StatusNotFound {
+		t.Errorf("GET /drawers/x/open = %d, want 404", rec.Code)
+	}
+}