cachet: Can't run tests, stalling on SymfonyQuestionHelper

Debian 8 with PHP 5.6.19. I git clone, composer install, run ./vendor/bin/phpunit, I get the phpunit version output but no tests get ran.

strace makes it look like SymfonyQuestionHelper is waiting for input, as the process tries to read from STDIN:

open("/home/andreas/dev/cachet/vendor/symfony/console/Helper/SymfonyQuestionHelper.php", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=3119, ...}) = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=3119, ...}) = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=3119, ...}) = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=3119, ...}) = 0
mmap(NULL, 3119, PROT_READ, MAP_SHARED, 4, 0) = 0x7f46b386b000
munmap(0x7f46b386b000, 3119)            = 0
close(4)                                = 0
read(0, 0x29569a0, 8192)                = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
read(0, 

I can’t find any information in any markdown files on how to setup and run tests, so I’ll just assume this is a bug.