test-strategy

name	test-strategy
description	Assess and recommend the appropriate testing strategy for Rust code - unit tests, property-based tests, fuzz tests, Kani model checking, or simulation testing Use when this capability is needed.
metadata	{"author":"ahrav"}

Test Strategy Assessment

Analyze code and recommend the optimal testing approach from this project's testing toolkit.

Testing Toolkit Available

Type	Tool	Feature Flag	Best For
Unit Tests	#[test]	None	Specific behavior, edge cases, regression tests
Property Tests	proptest	stdx-proptest	Invariants over input domains, mathematical properties
Fuzz Tests	cargo-fuzz	External	Security-critical parsing, untrusted input handling
Model Checking	Kani	kani	Memory safety proofs, absence of panics, formal verification
Simulation Tests	Project harnesses	See below	System-level invariants, scheduling, chunking, archive expansion

Simulation Harnesses

This project has five purpose-built deterministic simulation harnesses. Always consider whether new or changed code should be covered by one of these.

Harness	Location	Feature	Scope	When to Add Cases
Scanner Sim	src/sim_scanner/	sim-harness	End-to-end chunked scanning, overlap dedup, fault injection, ground-truth oracle	Any change to scanning pipeline, chunking logic, finding dedup, or file discovery
Scheduler Sim	src/scheduler/sim.rs	scheduler-sim	Work-stealing scheduler invariants, buffer pool, I/O depth, budget enforcement	Any change to scheduling, buffer management, permit accounting, or budget caps
Archive Sim	src/sim_archive/	sim-harness	Deterministic archive building (zip/tar/gzip), entry locators, path canonicalization	Any change to archive format support, entry path handling, or extraction logic
Git Scan Sim	src/sim_git_scan/	sim-harness	Commit graph traversal, pack I/O, watermark handling	Any change to git scanning, blob iteration, or commit history logic
Tiger Harness	src/tiger_harness.rs	tiger-harness	Chunking correctness via oracle comparison (root-span containment)	Any change to chunk splitting, overlap computation, or scan-scratch merging

Decision Framework

Use Unit Tests When:

• Testing specific, known edge cases
• Verifying exact output for exact input
• Regression tests for fixed bugs
• Simple function behavior verification
• Fast feedback during development

#[cfg(test)]
mod tests {
    #[test]
    fn specific_edge_case() {
        assert_eq!(function(edge_input), expected_output);
    }
}

Use Property-Based Tests (proptest) When:

• Function should satisfy invariants for ALL valid inputs
• Testing mathematical properties (commutativity, associativity, idempotence)
• Round-trip properties (encode/decode, serialize/deserialize)
• Relationship between functions (e.g., parse and format are inverses)
• Exploring large input spaces systematically

#[cfg(all(test, feature = "stdx-proptest"))]
mod prop_tests {
    use proptest::prelude::*;

    proptest! {
        #[test]
        fn roundtrip_property(input in any::<ValidInput>()) {
            let encoded = encode(&input);
            let decoded = decode(&encoded).unwrap();
            prop_assert_eq!(input, decoded);
        }
    }
}

Run with: cargo test --features stdx-proptest

Use Fuzz Tests When:

• Parsing untrusted or external input (files, network data)
• Security-critical code paths
• Looking for crashes, panics, or undefined behavior
• Complex state machines with many paths
• Finding inputs that cause pathological performance

// In fuzz/fuzz_targets/
#![no_main]
use libfuzzer_sys::fuzz_target;

fuzz_target!(|data: &[u8]| {
    let _ = parse_untrusted(data);
});

Run with: cargo +nightly fuzz run <target>

Use Kani Model Checking When:

• Proving absence of panics/undefined behavior
• Verifying memory safety in unsafe code
• Proving loop bounds and termination
• Exhaustive verification of small input spaces
• Critical algorithms where bugs are unacceptable

#[cfg(kani)]
mod verification {
    use super::*;

    #[kani::proof]
    fn verify_no_panic() {
        let x: u32 = kani::any();
        kani::assume(x < 1000);
        let result = critical_function(x);
        // Kani proves this never panics
    }

    #[kani::proof]
    #[kani::unwind(10)]
    fn verify_loop_bounds() {
        let arr: [u8; 8] = kani::any();
        process_array(&arr); // Prove no out-of-bounds
    }
}

Run with: cargo kani --features kani

Use Simulation Tests When:

• Testing system-level behavior that emerges from component interactions
• Verifying invariants under many possible interleavings or schedules
• Changes touch the scanning pipeline, scheduler, archive handling, or git scanning
• You need deterministic replay of failure cases
• Verifying that chunked scanning matches a single-pass oracle
• Testing fault tolerance (I/O errors, corruption, cancellation)
• Ensuring budget/cap enforcement across the full pipeline

Choosing the right harness:

Is it about how work gets scheduled, buffer pools, or permits?
  → Scheduler Sim (src/scheduler/sim.rs, feature: scheduler-sim)

Is it about scanning files, finding secrets, or chunking?
  → Scanner Sim (src/sim_scanner/, feature: sim-harness)
  → Also Tiger Harness if specifically about chunk boundary correctness

Is it about archive formats (zip/tar/gzip) or entry extraction?
  → Archive Sim (src/sim_archive/, feature: sim-harness)
  → Scanner Sim for end-to-end archive-then-scan flows

Is it about git blob scanning, commit traversal, or pack I/O?
  → Git Scan Sim (src/sim_git_scan/, feature: sim-harness)

Adding a corpus case (scanner sim example):

// tests/simulation/scanner_corpus.rs — add a new #[test] fn
#[test]
fn regression_my_new_edge_case() {
    let scenario = Scenario { /* ... */ };
    let config = RunConfig { /* ... */ };
    let outcome = sim_scanner::runner::run(&scenario, &config);
    assert!(outcome.is_success(), "{outcome:#?}");
}

Adding a corpus case (scheduler sim example):

// tests/simulation/scheduler_sim.rs
#[test]
fn my_new_scheduler_invariant() {
    let config = SimConfig { /* ... */ };
    let report = scheduler::sim::run(config, seed);
    report.assert_invariants();
}

Run with:

cargo test --features scheduler-sim --test simulation   # Scheduler only
cargo test --features sim-harness --test simulation      # Scanner + archive + git
cargo test --features sim-harness,scheduler-sim --test simulation  # All

Assessment Checklist

When analyzing code for test strategy, consider:

1. Input Domain

   • Fixed, known inputs → Unit tests
   • Large/infinite input space → Property tests
   • Untrusted/adversarial input → Fuzz tests
   • Small but critical input space → Kani
   • Interleaving-sensitive behavior → Simulation tests

2. Properties to Verify

   • Specific behavior → Unit tests
   • Invariants over all inputs → Property tests
   • "Never crashes" → Fuzz tests + Kani
   • Memory safety → Kani (especially for unsafe)
   • System-level invariants (no leaks, monotonic progress, ground truth) → Simulation tests

3. Code Characteristics

   • Pure functions → Property tests
   • Parsers/decoders → Fuzz tests
   • Unsafe blocks → Kani proofs
   • State machines → Property tests + Fuzz
   • Scanning pipeline components → Scanner Sim + Tiger Harness
   • Scheduler / buffer pool / permits → Scheduler Sim
   • Archive format handling → Archive Sim
   • Git blob / commit traversal → Git Scan Sim

4. Simulation Harness Checklist (always evaluate)

   • Does this change affect how files are discovered or scanned? → Scanner Sim
   • Does this change affect chunking, overlap, or finding dedup? → Scanner Sim + Tiger Harness
   • Does this change affect task scheduling, buffer management, or budget caps? → Scheduler Sim

Example Assessment Output

## Test Strategy for `WindowValidator`

### Recommended Approach: Property Tests + Kani + Scanner Sim

**Rationale:**
- Operates on sliding windows over byte streams (large input space)
- Has invariant: validated windows never exceed buffer bounds
- Contains unsafe pointer arithmetic
- Part of the scanning pipeline → needs sim coverage

**Specific Tests:**

1. **Property Test**: Window position invariants
   - Property: `window.end <= buffer.len()` for all inputs
   - Property: Windows never overlap incorrectly

2. **Kani Proof**: Memory safety of unsafe block
   - Prove: No out-of-bounds access in `unsafe` pointer ops
   - Bound: Unwind factor based on max window size

3. **Unit Tests**: Known edge cases
   - Empty buffer
   - Single-byte buffer
   - Window at buffer boundary

4. **Simulation**: Scanner Sim corpus case
   - Add scenario exercising the new window behavior under chunking
   - Tiger Harness: verify chunk boundaries don't lose findings
   - Verify oracle match (chunked result == single-pass result)

## Test Strategy for `ZipEntryIterator`

### Recommended Approach: Fuzz + Archive Sim + Scanner Sim

**Rationale:**
- Parses untrusted archive data (fuzz target)
- Changes archive extraction path → needs Archive Sim coverage
- End-to-end scanning of archive entries → needs Scanner Sim coverage

**Specific Tests:**

1. **Fuzz Test**: Parse arbitrary zip bytes without panic
2. **Archive Sim**: Corpus case with edge-case zip entries
   (long names, deflate truncation, encrypted entries)
3. **Scanner Sim**: End-to-end scenario: zip file → extract → scan → ground truth
4. **Unit Tests**: Known zip quirks (zip64, empty entries, duplicate names)

Quick Reference

Scenario	Primary	Secondary
New data structure	Property tests	Unit tests for edges
Parser/decoder	Fuzz tests	Property tests for roundtrip
Unsafe code	Kani proofs	Property tests for API
Algorithm correctness	Property tests	Unit tests for examples
Bug fix	Unit test (regression)	Sim corpus case if pipeline-related
Performance-critical loop	Kani (bounds)	Property tests
Scanning pipeline change	Scanner Sim	Tiger Harness for chunk correctness
Scheduler / buffer mgmt	Scheduler Sim	Unit tests for edge cases
Archive format handling	Archive Sim	Fuzz tests for untrusted input
Git scanning change	Git Scan Sim	Unit tests for specific commit patterns
Chunking / overlap logic	Tiger Harness	Scanner Sim for end-to-end
New file type support	Scanner Sim	Archive Sim if archive-based

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