What would be the reason for Coinbase and Circle sending $230 million USDC back and forth?

It started about 8 hours ago.

https://i.imgur.com/DgWoWhp.png

1. Coinbase sends $230 million USDC to Circle's deposit wallet:

https://etherscan.io/tx/0x2b9130c4b4949fa0b86a5c302557b0547e199454e67489fc6db16092d1056477

1. Circle moves the $230 million to another Circle wallet:

https://etherscan.io/tx/0x75f3b2e9931c3d28775364dc6f0a42dc56bb0ec3d225dc782905d505813b4c26

1. Circle then sends the $230 million to a null address:

https://etherscan.io/tx/0xa27f9e785297115d9e0cafc90da7ec0f73abbb1a8136ab1ef63d06cee77a386c

1. The null address sends $230 million USDC back to Circle:

https://etherscan.io/tx/0x625cbc9bc6361499d9fbdc04f5fd4684e371b25d86c2c86e535c64026a82893e

1. Circle then sends that $230 million USDC to Coinbase's USDC hot wallet:

https://etherscan.io/tx/0xeea161e6181fcacfe8c80fdf25ef9b9445933936b936abebd435571c0f00de48

This cycle repeats 4 times. Are they testing stuff?