Dev Capsem Doctor

capsem-doctor

capsem-doctor is a pytest-based diagnostic suite that runs inside the guest VM. It verifies sandbox integrity, network isolation, runtime environment, and AI agent functionality. It's the smoke test gate -- every change must pass it before shipping.

Doctor is also an Ironbank input. When doctor is used to close a

release-critical VM/security/protocol/package-manager gate, load /ironbank

and assert the full ledger through tests/ironbank/: client result, DB rows,

structured logs, UDS/HTTP route output, counters, and UI-facing JSON. A doctor

exit code or "row exists" check is not enough.

Running

just exec "capsem-doctor"              # Full suite (~10s total including VM boot)
just exec "capsem-doctor -k sandbox"   # Only sandbox tests
just exec "capsem-doctor -k network"   # Only network tests
just exec "capsem-doctor -x"           # Stop on first failure
just exec "capsem-doctor -v"           # Extra verbose

Test categories (11 files)

| File | What it validates |

|------|-------------------|

| test_sandbox.py | Read-only rootfs, binary permissions (chmod 555), no setuid/setgid, kernel hardening (no modules, no debugfs, no IPv6, no swap, no kallsyms), process integrity (pty-agent, dnsmasq running; no systemd, sshd, cron), network isolation (dummy0, fake DNS, iptables, no real NICs) |

| test_network.py | MITM CA in system store + certifi, curl without -k works, Python urllib HTTPS, CA env vars set (SSL_CERT_FILE, REQUESTS_CA_BUNDLE, NODE_EXTRA_CA_CERTS), HTTP/80 blocked, non-443 ports blocked, direct IP blocked, multi-domain DNS faking, AI provider domains reachable |

| test_environment.py | TERM/HOME/PATH env vars correct, shell is bash, kernel version, aarch64 arch, mount points (/proc, /sys, /dev, /dev/pts), tmpfs verification |

| test_runtimes.py | Python3, Node.js, npm, pip3, git version checks; Python file I/O; Node file I/O; git init+commit workflow |

| test_utilities.py | ~36 unix utilities available (coreutils, text processing, network, system tools, capsem-bench) |

| test_workflows.py | Text write/read, JSON roundtrip (Python + Node), shell pipes, large file (10MB) |

| test_ai_cli.py | claude, gemini, codex installed and executable without crashing |

| test_virtiofs.py | VirtioFS root mount, ext4 loopback upper, loop device active, workspace write/read/large file/subdir, system overlay writable, pip install works, file delete+recreate (skipped in block mode) |

| test_mcp.py | Guest MCP endpoint tool routing, domain blocking via MCP |

| test_injection.py | Security injection tests |

| conftest.py | Test infrastructure (auto-skip outside VM, run() helper, output dir fixture) |

Infrastructure (conftest.py)

# Auto-skip if not in capsem VM (checks root + writable /root)
def pytest_ignore_collect(collection_path, config):
    if os.geteuid() != 0 or not os.access("/root", os.W_OK):
        return True

# Shell command runner
def run(cmd, timeout=10):
    return subprocess.run(cmd, shell=True, capture_output=True, text=True, timeout=timeout)

# Shared output directory: /root/tests
@pytest.fixture
def output_dir():
    return TESTS_OUTPUT_DIR

Adding a new test

• Add test functions to the appropriate guest/artifacts/diagnostics/test_*.py file, or create test_<category>.py
• Use from conftest import run for shell commands, output_dir fixture for temp files
• Tests auto-skip outside the capsem VM (no special guards needed)
• just exec "capsem-doctor" picks up changes immediately (diagnostics repacked into initrd)
• For rootfs-baked changes: just _build-assets then just exec "capsem-doctor"

Where tests live on disk

• Source: guest/artifacts/diagnostics/test_*.py (in the repo)
• In rootfs: /usr/local/lib/capsem-tests/test_*.py (baked by Dockerfile.rootfs)
• In initrd: overrides rootfs copies via _pack-initrd (fast iteration)

Writing good diagnostic tests

• Test one thing per function. Name clearly: test_readonly_rootfs, test_ca_in_certifi
• Use run() for shell commands, check .returncode and .stdout/.stderr
• Set reasonable timeouts (default 10s). Network tests may need longer.
• Think adversarially: test what should be blocked, not just what should work
• For VirtioFS tests, skip gracefully in block mode: pytest.mark.skipif
• For Ironbank/release gates, do not skip. If a package manager, protocol, or

diagnostic dependency is unavailable, the product or harness is broken.

• Package-manager diagnostics must prove function, not installation presence:

run the installed binary/module and verify deterministic behavior.