Requirements Traceability in HIL - HIL Testing

Requirements Traceability in HIL Testing

Bidirectional Traceability Chain

  System Safety Requirement (HARA -> FSC -> TSR)
  e.g., TSR-ABS-001: ABS shall activate within 100 ms of wheel lockup
       |
       v (decomposed to)
  Software Safety Requirement (SSR)
  e.g., SSR-ABS-015: ABS_Control() shall set valves_open=TRUE within 2 task cycles
       |
       v (verified by)
  HIL Test Case
  e.g., TC-ABS-015: test_abs_activates_on_panic_brake (pytest)
       |
       v (produces)
  Test Result (PASS/FAIL with timestamp and ECU SW version)
  e.g., PASS at 2024-11-15 14:23, SW v2.3.1, HIL rig SCALEXIO-01

  FORWARD trace: TSR -> SSR -> test case (coverage = are all SSRs tested?)
  BACKWARD trace: test case -> SSR -> TSR (justification = why does this test exist?)

Traceability Implementation with pytest Markers

Pythontraceability_markers.py

#!/usr/bin/env python3
# Embed requirements traceability directly in pytest test functions
# using custom markers -- generates traceability matrix automatically

import pytest

# Register custom markers in conftest.py or pytest.ini
# pytest.ini:
# [pytest]
# markers =
#     req: marks test with requirement ID
#     asil: marks ASIL level of requirement under test

@pytest.mark.req("TSR-ABS-001", "SSR-ABS-015")
@pytest.mark.asil("ASIL-D")
def test_abs_activates_on_panic_brake(hil):
    """ABS shall activate within 100 ms of wheel lockup (TSR-ABS-001)"""
    hil.set("Plant/Speed_kph",       100.0); hil.wait(2.0)
    hil.set("Plant/Brakes/PedalPct", 100.0)
    assert hil.wait_signal("ECU.ABS.Active", lambda v: v > 0.5, 200)

# Traceability matrix generator: reads markers from test collection
def generate_traceability_matrix(session):
    matrix = []
    for item in session.items:
        req_mark  = item.get_closest_marker("req")
        asil_mark = item.get_closest_marker("asil")
        reqs = list(req_mark.args) if req_mark else []
        asil = asil_mark.args[0] if asil_mark else "QM"
        matrix.append({
            "test_id":    item.nodeid,
            "req_ids":    reqs,
            "asil":       asil,
            "result":     "PENDING",
        })
    return matrix

Summary

Requirements traceability is the evidence that every safety requirement has at least one test case, and every test case exists for a reason (it tests a specific requirement). Without bidirectional traceability, it is impossible to answer the auditor question: "which tests cover your ASIL-D safety requirements?" Embedding requirement IDs directly in test function markers (as shown above) enables automatic generation of the traceability matrix from the test suite itself - no manual spreadsheet maintenance required. The gap analysis (finding SSRs with no test case) becomes a simple query against the traceability matrix.

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.

🏭 How This Topic Appears in Production Projects

Project integration phase: The concepts covered in this lesson are most commonly encountered during ECU integration testing — when multiple software components from different teams are combined for the first time. Issues that were invisible in unit tests frequently surface at this stage.
Supplier/OEM interface: This is a topic that frequently appears in technical discussions between Tier-1 ECU suppliers and OEM system integrators. Engineers who can speak fluently about these details earn credibility and are often brought into critical design review meetings.
Automotive tool ecosystem: Vector CANoe/CANalyzer, dSPACE tools, and ETAS INCA are the standard tools used to validate and measure the correct behaviour of the systems described in this lesson. Familiarity with these tools alongside the conceptual knowledge dramatically accelerates debugging in real projects.

⚠️ Common Mistakes and How to Avoid Them

Assuming default configuration is correct: Automotive software tools ship with default configurations that are designed to compile and link, not to meet project-specific requirements. Every configuration parameter needs to be consciously set. 'It compiled' is not the same as 'it is correctly configured'.
Skipping documentation of configuration rationale: In a 3-year ECU project with team turnover, undocumented configuration choices become tribal knowledge that disappears when engineers leave. Document why a parameter is set to a specific value, not just what it is set to.
Testing only the happy path: Automotive ECUs must behave correctly under fault conditions, voltage variations, and communication errors. Always test the error handling paths as rigorously as the nominal operation. Many production escapes originate in untested error branches.
Version mismatches between teams: In a multi-team project, the BSW team, SWC team, and system integration team may use different versions of the same ARXML file. Version management of all ARXML files in a shared repository is mandatory, not optional.

📊 Industry Note

Engineers who master both the theoretical concepts and the practical toolchain skills covered in this course are among the most sought-after professionals in the automotive software industry. The combination of AUTOSAR standards knowledge, safety engineering understanding, and hands-on configuration experience commands premium salaries at OEMs and Tier-1 suppliers globally.