A bitcoind executable is required in order to run the RPC tests. In travis tests we download the version set in the test environment, and in the local environment the version can be set with an environment variable.
BITCOIND_PATH=/path/to/bitcoind vendor/bin/phpunit -c phpunit.rpc.xml
It can happen that a node can remain running if the tests
crash - keep an eye out for this, and if it happens killall -9 bitcoind
works, but make sure real nodes are shut down before hand!