PREEMPT_RT validation harness

Test cases verifying the PREEMPT_RT validation harness sub-feature (PREEMPT_RT validation harness (FEAT_0022)). These tests do not validate the absolute jitter envelope — that is a manual procedure per Documented reproducer proce... (REQ_0112) and Harness as xtask, not CI gate (ADR_0061). The tests below verify that the harness itself is well-formed (it builds, emits valid output, and agrees with the runtime’s own telemetry).

Test Case: Harness builds and runs on Linux non-RT TEST_0240
status: open
verifies: REQ_0111

Goal. The harness binary builds and runs to completion on a stock (non-PREEMPT_RT) Linux host without requiring elevated capabilities, and produces well-formed NDJSON on stdout.

Fixture. GitHub Actions Linux x86_64 runner; the harness is built with cargo build --release -p xtask-preempt-rt.

Steps.

  1. Build the harness in release mode.

  2. Run cargo run --release -p xtask-preempt-rt -- --load-profile idle --cycle-count 1000 --task-count 1 --scan-period-us 1000.

  3. Capture stdout; assert each line parses as JSON and contains the expected keys (ts_ns, task_id, period_ns, actual_period_ns, jitter_ns, took_ns).

  4. Assert the captured line count equals cycle-count.

Expected outcome. Smoke run succeeds; output is well-formed.

Lives under xtask/preempt-rt/tests/smoke.rs.
Test Case: NDJSON schema validation TEST_0241
status: open
verifies: REQ_0111

Goal. The harness output conforms exactly to the documented NDJSON schema; no extra keys, no missing keys, correct value types.

Fixture. An in-tree JSON Schema file (xtask/preempt-rt/schema/cycle-observation.schema.json) describes the record shape from Cyclictest-style benchmark ... (REQ_0111).

Steps.

  1. Run a short harness invocation (100 cycles).

  2. Validate every output line against the schema using a lightweight in-tree validator (no new workspace dep — match keys + value-type assertions manually).

  3. Assert all 100 lines validate.

Expected outcome. Output is schema-conformant.

Lives under xtask/preempt-rt/tests/schema.rs.
Test Case: Harness telemetry agrees with stats_snapshot TEST_0242
status: open
verifies: REQ_0113

Goal. The NDJSON cycle observations produced by the harness agree with Executor::stats_snapshot aggregates taken at the end of the run — i.e. the harness and the pull API see the same underlying data.

Fixture. A test variant of the harness that, after writing its last NDJSON line, also writes a single StatsSnapshot JSON record to stderr.

Steps.

  1. Run 1000 cycles with one cyclic task.

  2. Compute the percentile from the NDJSON took_ns column directly.

  3. Compare against the matching field in the stderr StatsSnapshot record.

  4. Assert agreement within the histogram-bucket bound (~1%).

Expected outcome. Push and pull paths agree on the same data.

Lives under xtask/preempt-rt/tests/push_pull_agreement.rs.