This error happened after a composer update and the codebase itself was fine but the tests were not, when creating a user in a factory the word password as a hash was being passed as a password rather than running the string through the bycrypt method but in this post I found an answer.

There are two files that set the rounds for the bycrypt method and they were different. config/hashing.php

'bcrypt' => [
'rounds' => env('BCRYPT_ROUNDS', 10),
],

and phpunit.xml

<php>
<env name="APP_ENV" value="testing"/>
<env name="BCRYPT_ROUNDS" value="4"/>
<env name="CACHE_DRIVER" value="array"/>
<env name="DB_DATABASE" value="testing"/>
<env name="MAIL_MAILER" value="array"/>
<env name="QUEUE_CONNECTION" value="sync"/>
<env name="SESSION_DRIVER" value="array"/>
<env name="TELESCOPE_ENABLED" value="false"/>
</php>

So by changing the phpunit.xml files BYCRYPT_ROUNDS value to the same as in the config/hashing.php file the tests then passed, until I change something else anyway.

<env name="BCRYPT_ROUNDS" value="10"/>