ERROR: docker run --rm -v $PWD/:/app composer/composer install

[rinetd]

Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Installation request for mockery/mockery 0.9.4 -> satisfiable by mockery/mockery[0.9.4].
- mockery/mockery 0.9.4 requires hamcrest/hamcrest-php ~1.1 -> no matching package found.

Potential causes:

• A typo in the package name
• The package is not available in a stable-enough version according to your minimum-stability setting
  see https://getcomposer.org/doc/04-schema.md#minimum-stability for more details.

Read https://getcomposer.org/doc/articles/troubleshooting.md for further common problems.

[alcohol]

This issue is unrelated to the container. Your lock file is out of sync with your composer.json, this can cause issues such as the one you are experiencing.