Docker Compose não pode iniciar o serviço PHP

Question

Quando executo docker-compose up -d no meu contêiner do Docker, recebo esses erros:

Starting test_php_1
test_mysql_1 is up-to-date

ERROR: for php  Cannot start service php: error while creating mount source path '/var/www/html/test': mkdir /var/www: read-only file system
ERROR: Encountered errors while bringing up the project.