dev-testing

name	dev-testing
description	Capsem testing policy and workflow. Use whenever running or writing tests. For VM, hypervisor, frontend, or Python specifics see the dev-testing-* skills.

Testing

Read tests/README.md before adding or moving test fixtures. Test-only config belongs under tests/fixtures/, not root config/.

Where a new guard belongs

A test that records an architectural mistake -- something that must not be repeated, checkable from source -- is a Citadel guard, in tests/citadel/, not another file at tests/ root. It runs in the fast phase, so it costs seconds rather than waiting on an asset build.

Two rules the existing guards follow:

State the reason in a named *_RATIONALE appended to the assertion, so a violation teaches. test_db_boundary.py is the model. Where the reason is already stated canonically -- config/gate.toml [boundary], AGENTS.md, a skill -- cite it instead of restating it.

Write the adversarial case, not just the conformance case. A guard proved only by inputs it was built for is not proved. test_workflow_enforcement.py carries fourteen evasions and four legitimate shapes because enumerating bad spellings let five through; the rule is now a whitelist for that reason.

Test execution

Command	What	VM?
just test	Everything: unit/coverage, cross-compile, frontend, Python/VM integration, injection, benchmarks, Linux install, and exact-package clean-Tart macOS install/glow-up	Yes
just fast-test	The fast gate itself; identical module to test and the release lanes	Yes
just vm-smoke	Repack, sign, boot, doctor, MCP, and service integration in a real VM	Yes

just test <commit> is the reusable release source of truth. just fast-test is useful developer feedback, but it never qualifies or releases anything. During TDD run the smallest native pytest, cargo, pnpm, or script command; release commands must consume the complete exact-commit journal.

The full gate is a construction boundary, not the edit loop. During TDD, reproduce the failure with the smallest focused test, run that test red/green, and batch adjacent parity fixes before paying for the complete gate. Run it once when the forward-fix source state is ready; any later production or gate change needs one new complete run.

just test deliberately accepts committed or uncommitted developer work. It records HEAD plus a digest of every tracked and untracked non-ignored source byte, then fails if either changes while the gate runs. Generated output stays under ignored build directories. The local proof therefore covers the exact source state the developer asked to test without forcing commit choreography. Automatic gate benchmark output belongs under ignored target/test-benchmarks/. Historical benchmark publication uses the owning pytest/benchmark command and an explicit review; it is not a Just convenience recipe.

Release CI invariant

Release CI reuses the same checked-in private modules as local just test:

• _test-fast
• _test-static
• _test-artifacts
• _test-functional
• _test-glowup
• _test-release-contracts

The build scope is selective; the quality scope is not. Binary CI builds only packages and resolves every channel profile by recorded digest. Profile CI builds exactly one channel/profile and resolves the current package by recorded digest. The resolved complementary artifacts are staged into the production test harness, not replaced by source-built substitutes.

Every activated pairing must pass artifact validation, all VM suites, Winterfell/MCP lifecycle, IronBank, injection, integration, benchmarks, full capsem-doctor, exact native install, and update glow-up. A staged profile whose minimum package is not yet satisfied may run only the self-consistency, integrity, isolation, and boot proof; the following binary lane must run the complete functional and glow-up modules before activation.

Both macOS and Linux must install their exact publishable native packages, including their real post-install scripts, before publication. Notarization and the public stable-to-nightly switch/upgrade glow-up remain mandatory end-to-end proof.

On Apple Silicon macOS, just test owns the pre-publication macOS package boundary through scripts/macos_release_glowup.py: it builds the package with the production assembler, installs that exact file in a disposable headless Tart guest, verifies the receipt, app bundle, complete binary cohort, service and gateway health, then extracts the same package on the physical Mac and boots a real Capsem guest VM from its exact binary/profile payload to a shell marker. The local package is unsigned; its postinstall ad-hoc signs the installed Mach-O payload with the required entitlements. Local qualification must not load Developer ID material or create a signing keychain. The tagged publication workflow alone signs, notarizes, staples, and installs the final publishable package. Tart macOS guests do not support nested virtualization, so these are two explicit halves of one script rather than a claimed nested proof. just fast-test deliberately excludes Tart and therefore cannot be used for release.

Rust is pinned to 1.97.1 across the workspace file, workflow steps, host-builder, and bootstrap. Change all pin surfaces together in a deliberate toolchain-bump PR. RustSec and JavaScript bulk advisories are blocking in just fast-test, local just test, ordinary CI, and both release lanes, as well as the scheduled/manual audit. A new advisory fails the candidate until it is remediated or explicitly reviewed in checked-in scanner policy.

Linux proof is host-aware: a cross-built non-host package receives structural validation in qualification and exact native installation in its tagged release job. CAPSEM_REQUIRE_LINUX_DEB_PROOF=1 must not reject that non-host package before the host package reaches its mandatory KVM proof. The hosted arm64 runner does not expose /dev/kvm, so it proves exact package/service operation while the x86_64 runner additionally owns the guest-shell marker.

Expensive harnesses need a cheap clean-environment bootstrap proof at the start of just test, before Docker/Colima or artifact preparation. The one private _test-fast module is also called by just fast-test, ordinary CI, and both release lanes. It owns YAML/workflow and source syntax, source contracts, dependency audits, Clippy, Python lint/type checks, and JavaScript/frontend checks; no caller may reproduce a subset inline. Only a green fast gate may build the Linux install-test image. That preflight must use a container-owned UV_PROJECT_ENVIRONMENT and prove python -m pytest launches before VM, package, or asset work consumes hours. Keep an ordering contract. It is fail-fast infrastructure validation only: the later Docker/systemd install E2E remains mandatory and must still exercise the installed package and post-install behavior.

Local/CI execution parity

Read references/local-ci-parity.md before editing any release workflow, gate recipe, or CI job. It holds the Ironbank parity rule (every portable release gate must be owned by just test), scanner/tool pinning, Docker platform and prune discipline, runtime/disk budgets, and the source-guard contracts.

TDD workflow

Write tests first:

1. Write failing tests that capture expected behavior
2. Verify they fail for the right reason
3. Write minimal implementation to pass them
4. Refactor

Without a failing test first, it's easy to write tests that pass by accident or don't actually verify the behavior you intended.

Functional slice proof matrix

Every non-trivial feature slice needs evidence in all of these categories before it can be called done. A green unit suite or a benchmark is not a substitute for functional or end-to-end proof.

Category	What it proves	Minimum expectation
Unit/contract	Pure logic, parser state machines, schema migration, helper APIs	Red/green tests for normal and edge behavior at the smallest useful boundary
Functional	The feature works through its production-facing API, not just private helpers	Exercise the real module boundary with realistic inputs and assert outputs plus side effects
Adversarial	The feature preserves security, privacy, and policy invariants when attacked	Malformed, oversized, denied, missing, racing, timeout, permission, and leak-prevention cases
E2E/VM	The user-visible path works in a real Capsem session	Boot/run a VM or use the black-box CLI/MCP/service path, then inspect externally visible behavior
Telemetry	Audit data is present, accurate, and queryable	Query session.db or logger readers for required rows, fields, decisions, errors, and attribution
Performance	Hot paths stayed inside the accepted budget	Benchmarks or timing assertions with recorded numbers and regression criteria

If a category is genuinely impossible or deliberately deferred, record it as missing with a reason, owner, and follow-up task. Silent deferral is the bug. "Covered by later E2E" is not enough unless the tracker names the later test and the current milestone is explicitly scoped as internal-only.

For policy, MITM, MCP, telemetry, networking, filesystem, process lifecycle, or sandbox-boundary work, the functional slice matrix is mandatory. The tests should prove not only that the happy path succeeds, but also that enforcement happens at the intended boundary: a blocked MCP tool does not dispatch, a blocked return does not leak, a denied URL does not reach the network, a malformed frame does not poison the stream, and telemetry records the truth.

Ironbank ledger tests

Use /ironbank for release-critical VM, network, model, MCP, credential broker, package-manager, doctor, benchmark, and security acceptance proof. Ironbank lives in tests/ironbank/ and is full black-box: tests are written from public contracts, CLI help, docs, generated schemas, hermetic fixtures, route responses, logs, DB rows, and installed package metadata. Do not inspect Rust/product internals to decide expected behavior.

Ironbank cannot use:

• skip, skipif, slow, optional markers, or public-network dependencies
• status-code-only replay
• row-exists checks
• parser-only assertions
• manual OAuth/client runs as release proof

One deterministic stimulus must prove the whole ledger path: client result, parsed facts, CEL/security decision, detection/enforcement rows, protocol DB rows, structured logs, status counters, UDS route, HTTP route, and UI-facing JSON. Every emitted DB/log/route field is exact-value asserted, covered by a typed invariant, or explicitly marked not applicable. Unknown fields fail the test until the field ledger is updated.

Package-manager tests prove function. Installing zstd, for example, means compressing known bytes, decompressing them, and comparing the exact output; not just checking dpkg output.

Logged-data DB ownership

Telemetry and security ledgers are database-owned. Service routes, UI handlers, MCP helpers, and benchmark harnesses must not build their own logged-data projection caches and must not open SQLite directly. They may own query intent (for example the fields a route needs), but they call the logger DB object to execute it. The logger DB object owns connection threads, mem/disk table layout, write buffering, flush, reload-from-disk behavior, WAL tuning, and future FTS5/search tables.

Do not move route-specific SQL into DbWriter or turn the DB layer into a pile of route helper methods such as stats_detail_payload() just to hide SQL. The boundary is execution and storage mechanics:

db.ready().await?;
db.query(sql, params).await?;
db.write(event).await?;

db.write(event).await means the DB object accepted the event into its producer buffer. Tests that assert read-after-write rows must use the DB flush barrier or shutdown/reopen. Do not paper over visibility with sleeps, route projections, or direct SQLite readers.

Empty table means empty result. Missing table or column means the schema contract is broken and must fail loudly; never add compatibility branches that treat missing ledger shape as empty data.

Regression tests must guard the boundary. If a route needs ledger data, add a test that proves the route uses the DB object and a source guard that rejects raw rusqlite opens, direct DbReader::open, and service-owned projection state in production route code. Add a companion guard that prevents route-specific DB writer methods or missing-schema fallbacks from being introduced.

Mock server boundary

crates/capsem-mock-server is the single reusable local fixture server for benchmarks, doctor, protocol recording/replay, gateway/integration tests, and Ironbank. It owns mock protocol responses and deterministic local upstream behavior. Tests may launch it through scripts/mock_server.py, tests/helpers/mock_server.py, or CAPSEM_MOCK_SERVER_BASE_URL.

Do not add another local HTTP/MCP/OAuth/model mock server for a feature. Extend the shared mock server and its fixtures instead, then assert the route through the relevant black-box test.

Parallel tests as dogfooding (n=4 is non-negotiable)

just test runs the python suite under pytest -n 4 --dist=loadfile. Four real VMs boot simultaneously. This is the canary, not just a speed-up. We ship Capsem as a multi-VM sandbox for AI agents -- if our own test suite cannot safely boot 4 concurrent VMs, real users running an agent farm will hit the exact same bug. Treat any concurrency flake as a Capsem-side bug, not a test-tuning problem:

• "Suspend timed out" under load -> service IPC handling is racy, not "bump the timeout"
• "Session did not become ready" -> Apple VZ resource serialization, VirtioFS lock contention, or service handling concurrent provisions; investigate, don't suppress
• Two tests both want the same VM name -> name-collision bug in validate_vm_name / registry, not "isolate test names better"
• Stale socket between tests -> service didn't reap a child cleanly, real production bug

Anti-patterns when a test flakes under -n 4:

• Adding time.sleep() to "let things settle" -- masking a race
• Bumping the per-test timeout -- buying time for a real bug to manifest in prod instead of CI
• Marking the test serial so it runs alone -- defeating the dogfooding signal

The exception is a true timing or benchmark probe whose assertion is the measured number. Those tests must already be marked serial and just test runs them immediately after the -n 4 canary. That is not a flake escape hatch: it prevents another benchmark file from stealing the same Apple VZ launch budget and corrupting the number we are trying to publish.

The host has plenty of headroom (48 GB RAM, 14 cores; 4 VMs at 2 GB / 2 CPU each = 8 GB / 8 cores). If concurrency surfaces a flake, fix the product, then re-run. Bumping -n higher (8, 12) is the natural follow-on once n=4 is stable -- real users will run more.

Orphan processes across runs are a product bug (not a test bug)

If a previous just test -n 4 run was interrupted (ctrl-C, pytest-xdist worker death, host crash) and the NEXT run flakes with "vm-ready never asserted", UDS "connection refused", or mysterious HTTP 500s -- the cause is companion processes from the interrupted run still alive under PID 1. pkill -f "target/debug/capsem-(service|process|gateway|tray|mcp)" will make the flake vanish, but that is cleanup-after-the-fact. The fix is on the COMPANION side: every spawned companion (gateway, tray, and any new one) must use capsem-guard::install(parent_pid, lock_path) to enforce (a) refuse-standalone, (b) singleton, (c) self-exit on parent death. See /dev-rust-patterns lesson 18. Regression tests live in tests/capsem-service/test_companion_lifecycle.py -- never remove them; when adding a new companion, extend that file.

Never pkill -f capsem- with a broad pattern during test debugging: capsem- matches --crate-name capsem-core in running rustc/cargo invocations and will SIGKILL the compiler mid-build. Use a binary-path pattern like pkill -f "target/debug/capsem-(service|process|gateway|tray|mcp)" instead.

Apple VZ lifecycle serialization is part of the product

Apple's Virtualization.framework does not tolerate overlapping checkpoint lifecycle operations (saveMachineStateToURL and restoreMachineStateFromURL) on sibling VMs, and teardown must not cross those checkpoint edges. Capsem uses ServiceState::save_restore_lock plus the host-wide VzHostLock flock: cold starts and teardown take shared/read guards, save and restore take exclusive/write guards. The rail holds even when pytest-xdist spawns one capsem-service per worker, while independent cold starts can still run together for the boot-latency gate.

Do not demote suspend/resume, lifecycle, provisioning, or teardown tests to -n 1 to sidestep VZ races. just test at -n 4 is the contract; if a concurrent run sees restore permission errors, loop-device corruption, connection-refused startup races, or readiness misses, fix the lifecycle rail. Full context and failure signatures live in docs/src/content/docs/gotchas/concurrent-suspend-resume.md.

Adversarial testing

Capsem is a security product. Every security-relevant feature needs tests that actively try to break invariants. Think like an attacker:

• Can a corp-blocked domain be snuck through another provider's list?
• Does an overlapping wildcard in allow+block always deny?
• Does malformed input (empty strings, unicode, huge payloads, invalid JSON) get rejected?
• Can path traversal escape the VirtioFS sandbox?
• Can a guest process modify its own binaries?

Stress-test boundary conditions. Write tests for the attacks you'd attempt yourself.

Security invariants to verify in tests

When touching security-relevant code, check these invariants have test coverage:

Invariant	What to test	Where
VirtioFS share is guest/ only	session_dir/guest/ exists, symlinks resolve, host-only files (session.db, serial.log) are outside the share	capsem-core::lib::tests
UDS sockets are 0600	After bind, verify permissions exclude other users	capsem-process
Process env is cleared	env_clear() called, only allowlisted vars passed	capsem-service spawn tests
No process::exit on guest I/O	Control channel close causes loop break, not exit	capsem-process
Sensitive logs are 0600	serial.log created with restricted permissions	capsem-process
Gateway auth on all routes	Every route except GET / returns 401 without token	capsem-gateway::auth::tests
Auth rate limiting	429 after threshold, resets after window	capsem-gateway::auth::tests
CORS rejects external origins	Only localhost/127.0.0.1/tauri allowed	capsem-gateway::tests
Body size limit	413 for >10MB payloads	capsem-gateway::proxy::tests
VM ID validation	Path traversal (../), dots, spaces, null bytes rejected	capsem-gateway::terminal::tests
Rootfs read-only	profile rootfs asset mounted ro, guest binaries 555	capsem-doctor in-VM tests
Suspend reports errors	IPC failure and timeout both return 500, not silent success	capsem-service tests

Test fixture anti-pattern: masking races with polling

If all test fixtures wait/poll before asserting, the tests will never catch server-side race conditions. For every endpoint that talks to a VM socket, write at least one test that calls it IMMEDIATELY after provision (no wait_exec_ready, no ready_vm fixture). The server must handle readiness internally.

Pattern to avoid (masks the bug -- server never needs wait logic because client always waits):

fixture calls provision -> fixture polls wait_exec_ready -> test calls exec

Required test pattern (catches the bug -- if server doesn't wait, test fails):

test calls provision -> test immediately calls exec -> server handles wait

See tests/capsem-service/test_svc_exec_ready.py for the regression tests that enforce this.

wait_exec_ready is a single call, not a loop

wait_exec_ready (in tests/helpers/service.py, tests/helpers/mcp.py, tests/capsem-gateway/test_gw_e2e.py) makes one exec call with the server-side timeout passed through. The server's handle_exec calls wait_for_vm_ready internally, which polls until the VM is ready. Do NOT add client-side retry loops -- that creates a double-wait where each retry can block for the full server timeout (30s client retries x 30s server wait = pathological cascade). One wait, one place.

Exec latency regression gate

tests/capsem-serial/test_boot_timing.py::test_exec_latency_within_gate asserts that provision-to-first-exec completes within EXEC_LATENCY_GATE. If this test fails, investigate boot time (process.log boot_timeline spans), not the wait mechanism.

Where tests live

• Rust unit: sibling tests.rs file, not inline mod tests { ... }. See the next subsection.
• Rust integration: crates/capsem-core/tests/
• In-VM diagnostics: guest/artifacts/diagnostics/test_*.py (see dev-testing-vm)
• Hypervisor: KVM + Apple VZ tests (see dev-testing-hypervisor)
• Frontend: frontend/src/lib/__tests__/ (see dev-testing-frontend)
• Python (builder): tests/test_*.py
• Python integration (service daemon): tests/capsem-*/ directories, each with its own conftest.py and pytest marker
• Ironbank release ledger: tests/ironbank/ (black-box only; no Rust implementation-derived expectations)

Rust unit tests: sibling tests.rs pattern

Every Rust module keeps its unit tests in a sibling tests.rs, not an inline mod tests { ... } block. The parent module declares:

// foo.rs  OR  foo/mod.rs
// ... production code ...

#[cfg(test)]
mod tests;

and the tests go in tests.rs in the same directory:

// tests.rs -- sibling of foo.rs or child of foo/
use super::*;

#[test]
fn roundtrip() { ... }

Why. Inline #[cfg(test)] mod tests { ... } blocks are appended at the bottom of prod files and commonly hit 50–99% of the file's line count. That means every Read, grep, and scroll to reach production code walks past thousands of test lines first. Several modules in this codebase hit 4,000+ lines that way before extraction. Agents and humans both read faster when prod code isn't buried.

Mechanics.

• tests.rs is a submodule of the parent file -- use super::*; works, private items are visible, #[cfg(test)] on the mod tests; declaration still gates compilation.
• For files that don't yet have a sibling directory (e.g. lib.rs, foo.rs), put tests.rs next to them in the same src/ directory.
• For files that are already foo/mod.rs, put tests.rs inside foo/.
• Attributes on the inline mod tests block (e.g. #[allow(unused_imports)]) move onto the declaration: #[cfg(test)]\n#[allow(unused_imports)]\nmod tests;.

Extraction recipe (for any remaining inline mod tests { ... }):

1. Move the block body (everything between the outer { and }) into a new sibling tests.rs.
2. Dedent one indentation level so contents read as top-level items.
3. Replace the old inline block with #[cfg(test)] mod tests; (plus any attributes that were on the original).
4. cargo test -p <crate> -- should pass identically.

When to push back. If you see a new PR or agent output adding an inline mod tests { ... } block, request it be moved to tests.rs before merge. Exceptions are narrow: tiny helper modules under ~50 lines total where inline tests plus prod code fit on one screen, or a module that's already a test-only helper.

Source contracts must read the sibling, not the production file

A Python contract asserting that some Rust test exists must read the sibling tests.rs, never the production .rs the test moved out of. Use tests/rust_sources.py:

from rust_sources import production, sibling_tests

assert "pub enum Status" in production(RELEASE_GRAPH)          # prod symbol
assert "release_graph_enums_reject_unknown" in sibling_tests(RELEASE_GRAPH)

Keep the two sources separate. Several contracts assert a symbol is absent from production ("Removed" not in source), and a test module legitimately names the thing it proves is rejected -- concatenating them lets a fixture falsify a claim about shipped code.

sibling_tests() resolves mod tests; the way Rust does (foo.rs → foo/tests.rs; main.rs/lib.rs/mod.rs → tests.rs beside it) and raises when the module is missing rather than passing on an empty string. The helper is not named tests_of on purpose: pytest collects test*, so the obvious name becomes a phantom failing test in every importer.

tests/test_rust_test_name_assertions.py enforces this repo-wide and fails in seconds. It resolves each assertion's target through the AST, per function scope, so a contract that legitimately names a relocated test while asserting it against a test module or spec document is not flagged.

Why it matters. This layout change broke sixteen contracts under tests/capsem-release/, then five more under tests/capsem-install/ that run only inside the Docker install gate -- invisible until forty minutes into a release run. Nothing about the failure pointed at a moved function; it read as a broken release.

Integration test suites

All Python integration tests live under tests/capsem-*/ and use pytest markers. Each suite has a dedicated just recipe.

Suite	Directory	Marker	VM?	What it tests
Service API	capsem-service/	integration	Yes	HTTP endpoints: provision, list, info, exec, logs, file I/O, delete
CLI	capsem-cli/	integration	Yes	CLI subcommands via subprocess
MCP	capsem-mcp/	mcp	Yes	MCP server black-box (stdio, tool routing)
Session DB	capsem-session/	session	Yes	Telemetry: net/model/tool/mcp/fs/snapshot events
Snapshots	capsem-snapshots/	snapshot	Yes	Auto/manual snapshots, revert
Isolation	capsem-isolation/	isolation	Yes	Multi-VM filesystem + network isolation
Security	capsem-security/	security	Yes	Binary perms, codesigning, asset integrity, env blocklist
Config	capsem-config/	config	Yes	Limits, resource bounds, hot-reload
Bootstrap	capsem-bootstrap/	bootstrap	No	Setup flow, dev tools, asset checks
Stress	capsem-stress/	stress	Yes	5 concurrent VMs, rapid create/delete
Build chain	capsem-build-chain/	build_chain	Yes	cargo build -> codesign -> pack -> manifest -> boot
Guest	capsem-guest/	guest	Yes	Network, services, filesystem, env inside guest

just test is the only public complete/release gate and just fast-test is the only public focused composite. Suite-specific and install/package rails are private implementation details; run an individual pytest/cargo/pnpm command directly for focused diagnosis instead of adding another public composite.

Public Just recipes, Capsem CLI command paths, and service HTTP method/path pairs are exact approval-gated surfaces. Any change must pass tests/test_public_surface_contract.py and requires explicit approval before editing config/public-surface.toml.

Test matrix: what runs where

Read references/test-matrix.md for the per-crate Rust CI matrix and the Python suite map (which suites run versus collect in PR CI, smoke, and the full gate).

Coverage targets

Component	Floor	Enforced	Where
Rust workspace	63%	--fail-under-lines 63	CI (cargo llvm-cov), just test
Python selected CI suite	85%	--cov-fail-under=85	Ordinary CI
Python full suite	85%	--cov-fail-under=85	just test
capsem-service	80%	Codecov component	codecov.yml
capsem-mcp	80%	Codecov component	codecov.yml
capsem-gateway	80%	Codecov component	codecov.yml
capsem (CLI)	80%	Codecov component	codecov.yml

Coverage

• Rust: cargo llvm-cov via just test (floor: 63% line coverage)
• Python: ordinary CI and the full just test suite both enforce 85%.
• codecov.yml maps components to code paths. Update it when files or directories are added, moved, or renamed.

Fast debug with capsem MCP tools

Read references/mcp-debug-tools.md for interactive VM debugging through the capsem MCP server: tool table, one-shot vs iterative workflows, and common session-DB queries. MCP tools are for fast targeted checks; just recipes are for comprehensive validation before committing.

End-to-end validation is not optional

After any change touching guest binaries, network policy, telemetry, MCP, or VM lifecycle:

1. just exec "capsem-doctor" -- verifies sandbox integrity inside the VM
2. After telemetry/logging changes: run a real session and verify with python3 scripts/check_session.py that net_events, model_calls, tool_calls, tool_responses, fs_events, dns_events, and security_rule_events are populated correctly for the exercised protocols

When tests fail

Never dismiss a test failure as "pre-existing" or "unrelated." Every failure must be investigated. Follow the dev-debugging workflow:

1. Do not change the test to make it pass. The test is evidence. Changing the assertion to match broken behavior destroys that evidence.
2. Reproduce and diagnose first. Understand why it fails before writing any fix. See the dev-debugging skill for the full methodology: reproduce with a test, diagnose root cause, then fix comprehensively.
3. Fix the code, not the test. If the test is genuinely wrong (not the code), explain in detail why the test's expectation is incorrect before changing it.

Measuring a gate's result

Never take the last line of a multi-part result as the result. Two shapes of one mistake, both of which report success while the thing measured failed:

$? after a pipe is the pipe's status. just test | tail reports what tail did. Redirect, then read the code separately:

just test > /tmp/gate.log 2>&1; echo "EXIT=$?"

tail -n1 across a multi-part result returns the last part, not the whole. cargo test -p capsem-service runs three test binaries; the last prints 0 passed, so | tail -1 reads as though the crate had no tests while 91 and 264 passed above it. Aggregate instead of sampling:

cargo test -p capsem-service 2>&1 | grep -E "^test result:"   # every binary

Both errors are silent and both flatter you: one turns a failed gate into a pass, the other turns a passing crate into a phantom regression. If a command can emit more than one verdict, read them all.

Read the first real error, not the recipe cascade under it — grep -aE "^FAILED|^E " lands on the cause, while the trailing error: Recipe ... failed lines are only the unwind.

tests/test_exit_status_integrity.py keeps this out of committed recipes, scripts, and workflows, and requires set -o pipefail in any bash recipe that pipes. It cannot see an agent's ad-hoc shell — that part is on you.

Fixtures use the wrapper, never the raw variable

Redirect Capsem paths with paths::CapsemPathsGuard::redirect(root). It sets CAPSEM_HOME, CAPSEM_RUN_DIR, and CAPSEM_ASSETS_DIR from one root and restores on drop, so a fixture cannot set one and inherit the rest.

Read logs with telemetry::read_log_tail, including in assertions: a test that opens a *.log path directly stops exercising what the product does the moment that stream rotates.

Both are enforced by tests/test_path_and_log_wrappers_are_mandatory.py. See /dev-rust-patterns "One rule, one function" for why.

Verify with the gate's environment, not a bare shell

just test exports CAPSEM_HOME, CAPSEM_RUN_DIR, CAPSEM_TEST_PROFILE, and CAPSEM_BENCHMARK_OUTPUT_ROOT. A test that reads ambient state passes in your shell and fails in the gate:

CAPSEM_HOME="$PWD/target/test-home/.capsem" \
CAPSEM_RUN_DIR="$PWD/target/test-home/.capsem/run" \
  cargo test -p <crate>

A fixture that overrides CAPSEM_HOME must override CAPSEM_RUN_DIR too — the run dir takes precedence over the home-derived default, so setting only the first sends production code to the ambient run directory while the fixture writes into a temp one. Bisect by exporting one variable at a time; that names the culprit in two runs instead of guessing.

Thresholds belong in one place

A number copied next to a rule drifts from it silently. Three separate gate failures in one session traced to this: a coverage floor asserted as 65 after it moved to 63, a guest kernel check demanding major >= 7 after the pin moved to 6.18, and a Docker fixture simulating 30 GiB free as "plenty" after the floor rose to 40.

Each read as a broken product, and each surfaced minutes-to-an-hour into a gate rather than at the edit. Derive the value from its source, or name it once and pin config and contract together:

floor = tomllib.loads(BUILD_CONFIG.read_text())["rails"]["assets"]["minimum_free_gib"]
ample_kib = (floor + 10) * 1024 * 1024   # follows the floor; never restates it

Prove it derives rather than hardcodes: change the source value and confirm the test follows instead of breaking.

Platform gating tests

cargo test --test platform_gating scans all .rs files under crates/ for macOS-only and Linux-only symbols (libc::clonefile, AppleVzHypervisor, KvmHypervisor, FICLONE, etc.) and verifies they appear inside #[cfg(target_os = "...")] blocks. This catches ungated platform APIs before they reach CI. Run this test when adding any platform-specific code.

Excluding something from a guard

Real trees contain things a guard should not fail on. One legal shape, in capsem.gate.exclusions: exact (the thing, not a category), hashed where the subject is content, with a stated reason whose length the schema checks, and reconciled both ways so a stale entry fails too. Never a count -- it fails on a harmless addition and passes on a dangerous change to something already listed. /dev-gate has why each wrong shape was tried.

Testable design

Extract logic into capsem-core -- never embed business logic in the app layer where it's coupled to Tauri. If you can't test something without booting a VM or launching the GUI, it belongs in core.