Required test-examples CI check fails for RLlib examples due to missing optional dependencies

[Sujit-Hiwale]

Summary

The required test-examples CI check currently fails for PRs that touch
RLlib example-related files because the example tests import optional
dependencies (ray, gymnasium) that are not installed in CI.

As a result, the test-examples job fails and blocks merging, even when
the PR itself does not modify test logic.

This issue builds on the installation problems discussed in #299, but focuses
specifically on the CI behavior and merge blocking.

---

Observed CI behavior

• test-examples is a required check for merging PRs.
• CI does not install examples/requirements.in.
• RLlib example tests under examples/rllib/ import Ray and Gymnasium at
  module import time.
• During CI:
  • tests fail with ModuleNotFoundError, or
  • the test job hangs or errors during collection.
• This causes test-examples to fail and prevents PRs from being merged.

Example failure from CI:

ERROR examples/rllib/self_play_train_test.py
ModuleNotFoundError: No module named 'ray'

---

Expected behavior

One of the following should be true:

• Example tests explicitly skip when optional dependencies are not installed, or
• CI installs the example dependencies before running test-examples, or
• Example tests are excluded from required CI checks.

In all cases, example-related tests should not cause mandatory CI failures
when optional dependencies are intentionally absent.

---

Additional context

PR #315 pins the RLlib example dependencies to a known-working set, addressing
runtime incompatibilities reported in #299. However, the PR is currently
blocked because test-examples fails due to the behavior described above.

This issue is intended to document the CI failure and discuss the preferred
long-term solution.

[matthewfearne]

I ran into this independently while working with Melting Pot for my DigiSoup project. The root cause is straightforward:

The test-examples workflow (test-examples.yml) calls .github/actions/install which runs bin/install.sh — that only installs core deps from requirements.txt. It never touches examples/requirements.in. Then CI runs pytest examples, which tries to collect examples/rllib/, hits bare imports of ray/gymnasium, and fails.

The cleanest fix would be adding pytest.importorskip() guards to the rllib test files:

# examples/rllib/self_play_train_test.py
ray = pytest.importorskip("ray")
from . import self_play_train

This way the tests skip gracefully when optional deps aren't installed, and actually run when they are. It's the standard pytest pattern for optional dependency tests and doesn't require changes to the CI workflow or making example deps mandatory.

Alternatively, CI could install examples/requirements.in in the test-examples job, but that pulls in ray/tensorflow/jax which adds significant install time and complexity to the workflow.