This configuration is valid only starting from Truffle v5.x:
On Truffle v4.x or earlier, you should change it to this:
When Ganache starts, it automatically unlocks the accounts specified in the command-line.
Will unlock the accounts with private keys
0x0...2 (2 accounts).
The default (if you don't specify anything) is
0x0...a (10 accounts).
GETH doesn't do that, so you must unlock the accounts yourself prior to running any of your Truffle tests, by sending to GETH an "unlock account" command for each one of the accounts used in these tests.