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Level 2: System Design ↔ System Testing

The second V-Model layer pairs System Design (left side) with System Testing (right side). While Level 1 validates what the system must do, this level validates how the system is structured to do it.

When to Use This Level

Use Level 2 when you need to:

  • Decompose requirements into concrete system components (subsystems, services, modules)
  • Define four IEEE 1016 design views for each component
  • Prove that every component is tested with named ISO 29119 techniques
  • Establish many-to-many traceability between requirements and components

Prerequisites

Level 2 requires requirements.md to exist. Run /speckit.v-model.requirements first.

Standards Alignment

IEEE 1016:2009 — Software Design Description

The system design uses four mandatory viewpoints:

Design View Description
Decomposition View System broken into components/modules with SYS-NNN IDs
Dependency View Relationships and coupling between components
Interface View External and internal interface contracts
Data Design View Data models, schemas, and data flow

ISO 29119-4 — Test Techniques

System tests use named techniques mapped to design views:

Design View Primary Technique What It Tests
Interface View Interface Contract Testing API contracts, protocol compliance, error responses
Data Design View Boundary Value Analysis Data limits, thresholds, ranges
Data Design View Equivalence Partitioning Representative data classes
Dependency View Fault Injection Failure propagation, graceful degradation

Commands

/speckit.v-model.system-design

Decomposes requirements into IEEE 1016-compliant system components with four mandatory design views and many-to-many REQ↔SYS traceability.

/speckit.v-model.system-design

What it produces:

  • A system-design.md file in specs/{feature}/v-model/
  • Every component gets a unique SYS-NNN ID
  • Each component maps to one or more parent REQ-NNN IDs (many-to-many)
  • Four design views: Decomposition, Dependency, Interface, Data Design
  • Component types: Subsystem | Module | Service | Library | Utility

/speckit.v-model.system-test

Generates ISO 29119-compliant system test cases with named techniques for every system component.

/speckit.v-model.system-test

What it produces:

  • A system-test.md file in specs/{feature}/v-model/
  • Test Procedures (STP-NNN-X) — logical test conditions per SYS-NNN
  • Test Steps (STS-NNN-X#) — executable step-by-step procedures
  • Each test case names its ISO 29119 technique explicitly

ID Schema

Tier ID Format Example Meaning
Design Element SYS-NNN SYS-001 A discrete system design element
Test Procedure STP-NNN-X STP-001-A A test procedure for SYS-001
Test Step STS-NNN-X# STS-001-A1 An executable test step for STP-001-A

Reading STS-001-A1 tells you: this step validates test procedure STP-001-A, which tests design element SYS-001. The same self-documenting lineage as the requirements level.

Inter-Level Linking

System components link upward to requirements via the Parent Requirements metadata field in the Decomposition View:

### SYS-003: Alert Engine

| Field | Value |
|---|---|
| **Parent Requirements** | REQ-001, REQ-005, REQ-NF-002 |
| **Type** | Service |
| **Description** | Evaluates sensor data against thresholds and triggers alerts |

This creates the inter-level trace: REQ-NNN → SYS-NNN → STP-NNN-X → STS-NNN-X#.

Many-to-Many Relationships

  • A single SYS may satisfy multiple REQs
  • A single REQ may be satisfied by multiple SYS components
  • The validator checks both directions

Validator

validate-system-coverage.sh

Validates bi-directional coverage across the REQ → SYS → STP → STS chain.

scripts/bash/validate-system-coverage.sh specs/<feature>/v-model

scripts/powershell/validate-system-coverage.ps1 specs/<feature>/v-model

Checks performed:

Check Direction What It Validates
Forward coverage REQ → SYS Every requirement maps to at least one system component
Backward coverage SYS → REQ Every component traces to an existing requirement
Test coverage SYS → STP → STS Every component has tests, every test has steps
No orphans STP → SYS No test procedures referencing non-existent components

Exit codes: 0 = full coverage, 1 = gaps found.

Partial mode

If system-test.md doesn't exist yet, the validator runs in partial mode — checking REQ → SYS forward coverage only and skipping SYS → STP → STS checks.

Matrix B: System Verification

Matrix B extends the traceability chain one level deeper:

  • Forward: REQ-NNN → SYS-NNN → STP-NNN-X → STS-NNN-X# (no gaps)
  • Backward: Every system test step → traces to a component → traces to a requirement (no orphans)

Matrix B proves that the system architecture is complete (every requirement is decomposed) and verified (every component is tested).