# Test Failures — Iteration 1a604562

## Summary
The coder's changes to increase Criterion configuration parameters (sample_size to 1000, measurement_time to 30s, warm_up_time to 5s) were **NOT sufficient** to achieve the AC4 requirement of CV < 5% for all three parser benchmarks. All three benchmarks failed the CV threshold test.

## Test Failures

### test_parser_simple_cv_below_5_percent
- **File**: `tests/test_parser_benchmarks.rs:107-140`
- **Error**: AC4 FAILED: parser_simple CV 8.88% exceeds 5% threshold
- **Expected**: CV < 5% (0.05)
- **Actual**: CV = 8.88% (0.0888)
- **Mean**: 1,194,856.58 ns (~1.19 ms)
- **Std Dev**: 106,122.63 ns (~0.106 ms)
- **Impact**: CRITICAL - Fails acceptance criteria AC4

### test_parser_complex_cv_below_5_percent
- **File**: `tests/test_parser_benchmarks.rs:142-176`
- **Error**: AC4 FAILED: parser_complex CV 39.04% exceeds 5% threshold
- **Expected**: CV < 5% (0.05)
- **Actual**: CV = 39.04% (0.3904)
- **Mean**: 4,216,069.37 ns (~4.22 ms)
- **Std Dev**: 1,646,068.94 ns (~1.65 ms)
- **Impact**: CRITICAL - Fails acceptance criteria AC4 by a very large margin (7.8x over threshold)

### test_parser_variables_cv_below_5_percent
- **File**: `tests/test_parser_benchmarks.rs:178-212`
- **Error**: AC4 FAILED: parser_variables CV 6.45% exceeds 5% threshold
- **Expected**: CV < 5% (0.05)
- **Actual**: CV = 6.45% (0.0645)
- **Mean**: 932,896.54 ns (~0.93 ms)
- **Std Dev**: 60,192.27 ns (~0.060 ms)
- **Impact**: CRITICAL - Fails acceptance criteria AC4

## Root Cause Analysis

The fundamental issue is that the benchmarks are measuring 12,000 iterations per sample, which creates a **total time per sample** that is very large (~1-4ms). This high total time is subject to:

1. **System noise**: OS scheduler interruptions, background processes
2. **Thermal throttling**: CPU frequency adjustments during long runs
3. **Cache effects**: Cache line evictions during large iteration counts
4. **Memory bandwidth**: Token cloning 12,000 times per sample stresses memory subsystem

The current approach of using 12,000 iterations to "dominate system noise" is counterproductive because:
- The measurement overhead becomes negligible compared to the operation itself
- But the **variance introduced by long measurement times** (system interference) becomes dominant
- This is especially problematic for `parser_complex` which has 39% CV

## Recommended Fix

The coder needs to reconsider the benchmarking strategy:

### Option 1: Reduce iteration count
Instead of 12,000 iterations, use **100-500 iterations** per sample. This:
- Keeps sample time reasonable (~10-200µs per sample)
- Reduces exposure to system interference
- Still amortizes measurement overhead sufficiently for fast operations

### Option 2: Remove iteration loop entirely
Let Criterion handle the iteration count automatically. The pre-tokenization outside the benchmark is correct, but the inner loop can be simplified:

```rust
c.bench_function("parser_simple", |b| {
    b.iter(|| {
        let tokens_clone = tokens.clone();
        let result = parser::parse(black_box(tokens_clone));
        black_box(result)
    });
});
```

Criterion will automatically run enough iterations to get stable measurements.

### Option 3: Increase warmup and measurement time further
- Increase warm_up_time to 10s
- Increase measurement_time to 60s
- This gives more time for CPU to stabilize and thermal effects to settle

## Test Coverage Assessment

### Covered Acceptance Criteria:
- ✅ **AC1**: Create benches/parser_benchmarks.rs with parser_simple, parser_complex, parser_variables benchmarks - COVERED by `test_all_three_parser_benchmarks_configured`
- ✅ **AC2**: Pre-tokenize input outside benchmark loop - COVERED by `test_parser_benchmarks_pretokenize_verification`
- ✅ **AC3**: Criterion generates estimates.json for each benchmark - COVERED by `test_parser_simple_benchmark_exists`, `test_parser_complex_benchmark_exists`, `test_parser_variables_benchmark_exists`
- ❌ **AC4**: CV < 5% for all benchmarks - COVERED but FAILING by `test_parser_simple_cv_below_5_percent`, `test_parser_complex_cv_below_5_percent`, `test_parser_variables_cv_below_5_percent`

### Edge Cases Covered:
The existing test suite includes comprehensive edge case coverage:
- ✅ Empty input handling
- ✅ Deeply nested expressions
- ✅ All arithmetic operators
- ✅ Multiple statements
- ✅ Invalid syntax error handling
- ✅ Criterion configuration validation

**No additional edge case tests are needed** - the test coverage is excellent.

## Passing Tests Summary
- 12 out of 15 tests passed
- All structural tests passed (file exists, benchmarks configured, pre-tokenization verified)
- All edge case tests passed
- All AC3 tests passed (estimates.json files exist and are valid)
- **Only CV threshold tests (AC4) failed**

## Test Results
```
test result: FAILED. 12 passed; 3 failed; 0 ignored; 0 measured; 0 filtered out
```

Total failures: **3 critical failures** (all related to AC4 - CV threshold)
