if e, g := 1, len(keys); e != g {
		t.Fatalf("after first response, expected %d idle conn cache keys; got %d", e, g)
	}
	addr := ts.Listener.Addr().String()
	cacheKey := "|http|" + addr
	if keys[0] != cacheKey {
		t.Fatalf("Expected idle cache key %q; got %q", cacheKey, keys[0])
	}
	if e, g := 1, tr.IdleConnCountForTesting("http", addr); e != g {
		t.Errorf("after first response, expected %d idle conns; got %d", e, g)
	}