# Verification Note for bf-18a0w: Improve Assertion Messages and Verify Test Correctness

## Summary
Improved assertion messages across all tests in `cmap_unmapped_glyphs.rs` to provide maximally helpful failure diagnostics. All 7 tests pass successfully.

## Changes Made

### File Modified
- `crates/pdftract-core/tests/cmap_unmapped_glyphs.rs`

### Assertion Message Improvements

#### Test 1: `test_cmap_unmapped_glyph_skip`
Enhanced assertion messages for:
- `is_unmapped_glyph_name()` checks - Added detailed failure messages explaining expected vs found and why this matters
- `map.is_empty()` check - Explains why empty map indicates parser error
- `map.len()` check - Details expected count and why incorrect count matters
- `map.lookup()` checks - Added expected/found/why matters for each lookup
- Unicode destination validation loop - Enhanced message about replacement character detection

#### Test 2: `test_cmap_multiple_mappings_with_unmapped_check`
Enhanced assertion messages for:
- `map.len()` check - Added context about beginbfchar...endbfchar parsing
- Individual mapping lookups (0x00, 0x01, 0x02) - Added expected/found/why matters for each
- `is_unmapped_glyph_name()` check - Explains function should not be affected by parsing

#### Test 3: `test_cmap_range_mapping_with_unmapped_awareness`
Enhanced assertion messages for:
- Range expansion check - Explains beginbfrange...endbfrange behavior and why 26 mappings expected
- First/last entry checks - Added context about Unicode code points (U+0041 for A, U+005A for Z)
- Unmapped glyph name checks - Clarified leading slash handling

#### Tests 4-7: Already had excellent assertion messages
These tests already had detailed, helpful assertion messages from previous work:
- `test_differences_overlay_filters_unmapped_glyphs`
- `test_differences_overlay_consecutive_with_unmapped_filtering`
- `test_differences_overlay_filters_null_glyph`
- `test_differences_overlay_filters_all_g_series_unmapped`

## Assertion Message Pattern

All assertion messages now follow this pattern for maximum helpfulness:
1. **What was expected** - Clear statement of the expected result
2. **What was found** - The actual result (using `{:?}` formatting for complex values)
3. **Why this matters** - Context about the assertion's purpose and implications

Example:
```rust
assert_eq!(
    map.len(),
    3,
    "CMAP should have exactly 3 mappings. \
     Expected: 3 mappings (A, B, C). \
     Found: {} mappings. \
     Why this matters: Incorrect mapping count indicates the parser is incorrectly \
     handling the beginbfchar...endbfchar construct.",
    map.len()
);
```

## Test Results

All 7 tests pass successfully:
```
running 7 tests
test test_cmap_multiple_mappings_with_unmapped_check ... ok
test test_cmap_range_mapping_with_unmapped_awareness ... ok
test test_cmap_unmapped_glyph_skip ... ok
test test_differences_overlay_consecutive_with_unmapped_filtering ... ok
test test_differences_overlay_filters_null_glyph ... ok
test test_differences_overlay_filters_all_g_series_unmapped ... ok
test test_differences_overlay_filters_unmapped_glyphs ... ok

test result: ok. 7 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
```

## Verification of Skip Behavior

The tests correctly verify the skip behavior through:
1. **Positive assertions** - Normal glyphs (A, B, C, space, CustomA, CustomB, Z) ARE present in CMAP output
2. **Negative assertions** - Unmapped glyphs (g001-g003, g000-g009, .notdef, .null) are ABSENT from CMAP output
3. **Configuration awareness** - Tests reference `build/unmapped-glyph-names.json` to explain why glyphs should be filtered

## Edge Cases and Limitations

### Edge Cases Covered
- Consecutive name assignments in /Differences arrays
- Leading slash on glyph names (/.notdef vs .notdef)
- Range mapping (beginbfrange...endbfrange)
- Multiple individual mappings (beginbfchar...endbfchar)
- Complete filtering (all entries are unmapped)

### Known Limitations
- Tests use hardcoded CMAP data structures rather than real PDF files
- Tests do not cover every possible CMAP format variation (focus on common cases)
- Tests assume `build/unmapped-glyph-names.json` contains the expected unmapped glyph names

## Acceptance Criteria Status

✅ **All assertion messages are clear and specific**
- Every assertion now follows the expected/found/why matters pattern
- Messages provide context about configuration (e.g., referencing build/unmapped-glyph-names.json)

✅ **Test runs without panics or errors**
- All 7 tests complete successfully with no errors

✅ **Test correctly identifies skip behavior**
- Positive assertions verify normal glyphs are preserved
- Negative assertions verify unmapped glyphs are filtered
- Tests use the actual `is_unmapped_glyph_name()` and `DifferencesOverlay::parse()` functions

✅ **Test provides helpful diagnostics on failure**
- Assertion messages explain what went wrong, what was expected, and why it matters
- Complex values are formatted using `{:?}` for easy debugging

## Commit Information

**Commit:** `bf-18a0w` - Improve assertion messages and verify test correctness

**Files Changed:**
- `crates/pdftract-core/tests/cmap_unmapped_glyphs.rs`

**Test Verification:** All 7 tests in cmap_unmapped_glyphs pass (0.00s)