if e, ok := alt.(erringRoundTripper); ok {
				// pconn.conn was closed by next (http2configureTransports.upgradeFn).
				return nil, e.RoundTripErr()
			}
			return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt}, nil
		}
	}

	pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
	pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())

	go pconn.readLoop()

}

// The lookupCache caches ArrayOf, ChanOf, MapOf and SliceOf lookups.
var lookupCache sync.Map // map[cacheKey]*rtype

// A cacheKey is the key for use in the lookupCache.
// Four values describe any of the types we are looking for:
// type kind, one or two subtypes, and an extra integer.
type cacheKey struct {
	kind  Kind
	t1    *abi.Type
	t2    *abi.Type
	extra uintptr
}

	t.Helper()

	transformer, encObject, cacheKey, err := envelopekmsv2.GenerateTransformer(testContext(t), "", &testKMSv2EnvelopeService{keyID: keyID}, useSeed)
	if err != nil {
		t.Fatal(err)
	}
	return envelopekmsv2.State{
		Transformer:         transformer,
		EncryptedObject:     *encObject,
		ExpirationTimestamp: exp,
		CacheKey:            cacheKey,
	}
}