Regjit Testing

RegJIT Testing

Overview

Write comprehensive tests for RegJIT regex engine to ensure correctness, prevent regressions, and verify compatibility with reference engines (PCRE, std::regex, RE2).

When to Use

• After implementing new features
• Before committing code
• When fixing bugs (write test first)
• When refactoring regex behavior
• When verifying anchor/quantifier edge cases

Test Types

Unit Tests

Test individual components in isolation

Example: Character matching

Initialize();
CompileRegex("a");
assert(Execute("a") == 1);      // Match
assert(Execute("b") == 0);      // No match
CleanUp();

Integration Tests

Test full compilation pipeline with realistic patterns

Example: Anchor quantifier

Initialize();
CompileRegex("^+");
assert(Execute("") == 1);       // Match at start
assert(Execute("xyz") == 1);    // Match at start
CleanUp();

Edge Case Tests

Test boundary conditions and special scenarios

Example: Empty string and boundaries

Initialize();
CompileRegex("^$");
assert(Execute("") == 1);       // Match empty
assert(Execute("x") == 0);      // Non-empty fails
CleanUp();

RegJIT Test Structure

Template

#include "../src/regjit.h"
#include <iostream>
#include <cassert>

int main() {
    std::cout << "[Feature Name Tests]" << std::endl;
    
    // Test case 1
    Initialize();
    CompileRegex("pattern");
    assert(Execute("input") == expected);
    CleanUp();
    
    // Test case 2
    Initialize();
    CompileRegex("pattern2");
    assert(Execute("input2") == expected2);
    CleanUp();
    
    std::cout << "[All tests passed]" << std::endl;
    return 0;
}

Test File Naming

• test_anchor.cpp - Anchor features (^, $, \b, \B)
• test_charclass.cpp - Character classes ([abc], [a-z])
• test_quantifier.cpp - Quantifiers (*, +, {n})
• test_anchor_quant_edge.cpp - Anchor + quantifier combinations

Test Categories for RegJIT

1. Anchor Tests

✅ ^ (start anchor)
   - Matches at position 0
   - With quantifiers: ^*, ^+, ^{n}
   
✅ $ (end anchor)
   - Matches at string length
   - With quantifiers: $*, $+, ${n}
   
✅ \b (word boundary)
   - Between \w and \W characters
   - With quantifiers: \b*, \b+
   
✅ \B (non-word boundary)
   - NOT between \w and \W
   - With quantifiers: \B*, \B+

2. Character Class Tests

✅ [abc] - Character set
✅ [a-z] - Range matching
✅ [^abc] - Negated class
✅ [a-zA-Z0-9] - Multiple ranges
✅ . - Any character

3. Quantifier Tests

✅ * - Zero or more (greedy)
✅ + - One or more (greedy)
✅ ? - Zero or one
✅ {n} - Exactly n times
✅ {n,} - At least n times
✅ {n,m} - Between n and m times
✅ *? - Zero or more (non-greedy)
✅ +? - One or more (non-greedy)

4. Combination Tests

✅ Anchors + Quantifiers
✅ Character class + Quantifiers
✅ Alternation + Anchors
✅ Groups + Features

Writing Good Tests

Principle 1: Clear Intent

// GOOD - Intent clear
assert(Execute("a") == 1);      // Single char matches

// UNCLEAR - Intent obscured
assert(1 == Execute("a"));      // Backwards, hard to read

Principle 2: Test One Thing

// GOOD - Single behavior
Initialize();
CompileRegex("a+");
assert(Execute("aaa") == 1);
CleanUp();

// WRONG - Multiple behaviors mixed
Initialize();
CompileRegex("a+");
assert(Execute("aaa") == 1 && Execute("b") == 0);
CleanUp();

Principle 3: Edge Cases Matter

// Pattern: [a-z]+
Initialize();
CompileRegex("[a-z]+");
assert(Execute("") == 0);           // Empty
assert(Execute("a") == 1);          // Minimum
assert(Execute("abc") == 1);        // Normal
assert(Execute("z") == 1);          // Boundary
assert(Execute("A") == 0);          // Outside range
assert(Execute("a1b") == 0);        // Non-matching char
CleanUp();

Principle 4: Verify Against Reference

// After writing test, verify with PCRE:
// pcre: [a-z]+ matches "abc" ✓
// pcre: [a-z]+ does NOT match "A" ✓
// Our implementation matches PCRE ✓

Test Execution

Building Tests

# Specific test
make test_anchor_quant_edge

# Run test
./test_anchor_quant_edge

# All tests
make test_all

Common Commands

# Build specific test
make test_charclass

# Run after building
./test_charclass

# Clean and rebuild
make clean && make test_all

# View test output
make test_anchor 2>&1 | tail -20

PCRE/RE2 Compatibility Testing

Verification Checklist

• Test matches PCRE behavior
• Test matches std::regex behavior
• Test matches RE2 behavior
• Document any intentional differences
• Add test to RegJIT suite

Example: Anchor Quantifier Compatibility

// Pattern: $+
// Expected: Matches only at end, but attempts at all offsets

// PCRE: $+ on "abc" matches at position 3 ✓
// std::regex: $+ on "abc" matches ✓
// RE2: $+ on "abc" matches ✓
// RegJIT: Our implementation matches ✓

Initialize();
CompileRegex("$+");
assert(Execute("abc") == 1);
CleanUp();

Test Maintenance

When to Add Tests

• Every new feature gets tests
• Every bug fix includes regression test
• Every compatibility change verified
• Every optimization needs performance test

When to Update Tests

• When refactoring matching logic
• When changing quantifier behavior
• When modifying anchor semantics
• When fixing a bug

When to Remove Tests

• Dead features removed
• Test infrastructure changed
• Duplicate test coverage consolidated

Quick Reference

Success Criteria

• All tests compile without warnings
• All tests pass (exit code 0)
• No memory leaks
• Tests are independent
• Coverage > 80%
• PCRE/RE2 compatible
• Comments explain purpose
• Ready to commit

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