Is there an active testnet for Bitcoin Cash? To learn more about Bitcoin Cash, I would like to try some things on the testnet.  I installed bitcoin-abc, made a copy of an existing datadir from a Bitcoin Core testnet install, and ran bitcoin-abc -testnet -reindex.  It got as far as:

2017-08-08 15:54:14 UpdateTip: new best=00000000f17c850672894b9a75b63a1e72830bbd5f4c8889b5c1a80e7faef138 height=1155875 version=0x20000000 log2_work=69.338231 tx=14689192 date='2017-08-01 13:58:35' progress=0.993792 cache=154.7MiB(460629tx)
2017-08-08 15:54:14 ERROR: AcceptBlock: bad-txn-replay, non playable transaction (code 16) (block 00000000000005063e35114c186ffd196272310fbe8265012ba0151eef092430)
2017-08-08 15:54:14 Misbehaving: 80.100.203.151:18333 peer=1 (0 -&gt; 10) reason: bad-txn-replay
2017-08-08 15:54:14 ERROR: ProcessNewBlock: AcceptBlock FAILED


I presume this is where the fork happened.  However, the client does not seem to be receiving any further blocks beyond this point.  It seems that many peers are being rejected as "misbehaving", presumably because they are really BTC nodes on the other branch of the fork.  (Though there are a lot of receive version message entries in the log that are not followed by Misbehaving.)

Are active transactions and mining taking place on the Bitcoin Cash testnet?  If so, how can I connect to nodes that know about it?  If not, why not?
Yes, there is.  After many hours I eventually received blocks up to the present time.  

There is a working DNS seed at testnet-seed-abc.bitcoinforks.org (hardcoded in the Bitcoin ABC source) which lists active Bitcoin Cash testnet nodes, many of which actually work.  Bitcoin ABC doesn't seem to prefer this seed - it tries lots of others that only have Bitcoin Core testnet nodes - but you can do manually do dig testnet-seed-abc.bitcoinforks.org and then addnode the resulting IP addresses.