Figured it out. The
config.edn file on the classpath (in ‘resources’ for that env) must contain something. An empty map is not sufficient. Once you set a k/v pair, the config will load. For db credentials in this case, GitLab allows you to set up a postgres service with ‘trust’ auth method.
If there’s a better way, please let me know. Perhaps using ‘real’ credentials in the ‘test’ config file, and using those in place of the ‘trust’ auth method?
Update: the simplest approach that works was to put a :database-url in the config.edn for the test env (which ensures the file is not empty) and configure the db that way rather than an environment variable.