Add check_test_files.py tool to detect and fix double newline endings in test files

- Create check_test_files.py with list and fix functionality
- Update tools/README.md with new tool documentation
- Support --fix flag for automatic repair
- Support --verbose flag for detailed output

Author: lufftw

tools/README.md

@@ -10,6 +10,7 @@ Developer tools for checking, validating, and generating project content.
 |----------|------|---------|
 | **Checking** | [`check_solutions.py`](#check_solutionspy) | Validate solution file architecture compliance |
 | | [`run_format_tests.py`](#run_format_testspy) | Run format unit tests |
+| | [`check_test_files.py`](#check_test_filespy) | Check and fix test files with double newline endings |
 | **Generation** | [`generate_mindmaps.py`](#generate_mindmapspy) | Rule-based mind map generation |
 | | [`generate_mindmaps_ai.py`](#generate_mindmaps_aipy) | AI-powered mind map generation |
 | | [`generate_pattern_docs.py`](#generate_pattern_docspy) | Pattern documentation generation |
@@ -43,6 +44,7 @@ python tools/generate_pattern_docs.py
 tools/
 ├── README.md                      # This file
 ├── check_solutions.py             # Solution file checker
+├── check_test_files.py            # Test file format checker/fixer
 ├── run_format_tests.py            # Format test runner
 ├── run_format_tests.bat/.sh       # Format test scripts
 │
@@ -131,6 +133,33 @@ tools\run_format_tests.bat     # Windows
 tools/run_format_tests.sh      # Linux/Mac
 ```
 
+### `check_test_files.py`
+
+Check and fix double newline ending errors in test files under `tests/` directory.
+
+Checks all `.in` and `.out` files to find files ending with two newlines (`\n\n`).
+
+```bash
+python tools/check_test_files.py              # List problematic files
+python tools/check_test_files.py --fix        # List and auto-fix
+python tools/check_test_files.py --verbose    # Show detailed info
+```
+
+**Features:**
+- List all test files ending with two newlines
+- Auto-fix: Remove extra newline, keep only one
+
+**Example Output:**
+```
+Found 3 files ending with two newlines:
+
+  tests/0977_squares_of_a_sorted_array_1.in
+  tests/0977_squares_of_a_sorted_array_1.out
+  tests/0142_linked_list_cycle_ii_1.in
+
+Tip: Use --fix to automatically fix these issues.
+```
+
 ---
 
 ## 🧠 Mind Map Generation

tools/check_test_files.py

@@ -0,0 +1,144 @@
+#!/usr/bin/env python3
+"""
+Check and fix double newline ending errors in test files under tests/ directory.
+
+Checks all .in and .out files to find files ending with two newlines (\n\n).
+
+Features:
+1. List problematic files
+2. Fix these files (remove extra newline)
+
+Exit Codes:
+- 0: All files OK or fix successful
+- 1: Errors found but not fixed
+
+Usage:
+    python tools/check_test_files.py              # List problematic files
+    python tools/check_test_files.py --fix        # List and fix
+    python tools/check_test_files.py --verbose    # Show detailed info
+"""
+import sys
+from pathlib import Path
+from typing import List
+
+
+PROJECT_ROOT = Path(__file__).parent.parent
+TESTS_DIR = PROJECT_ROOT / "tests"
+
+
+def check_file(file_path: Path) -> bool:
+    """
+    Check if file ends with two newlines.
+    
+    Returns:
+        True if file ends with \n\n (problematic)
+        False if file is OK
+    """
+    try:
+        with open(file_path, 'rb') as f:
+            data = f.read()
+            # Check if ends with \n\n
+            return data.endswith(b'\n\n')
+    except Exception as e:
+        print(f"Error: Cannot read file {file_path}: {e}", file=sys.stderr)
+        return False
+
+
+def fix_file(file_path: Path) -> bool:
+    """
+    Fix file: remove extra newline at end, keep only one.
+    
+    Returns:
+        True if fix successful
+        False if fix failed
+    """
+    try:
+        with open(file_path, 'rb') as f:
+            data = f.read()
+        
+        # If ends with \n\n, remove one \n
+        if data.endswith(b'\n\n'):
+            # Remove last \n
+            fixed_data = data[:-1]
+            
+            with open(file_path, 'wb') as f:
+                f.write(fixed_data)
+            return True
+        return False
+    except Exception as e:
+        print(f"Error: Cannot fix file {file_path}: {e}", file=sys.stderr)
+        return False
+
+
+def find_test_files() -> List[Path]:
+    """Find all .in and .out test files."""
+    if not TESTS_DIR.exists():
+        print(f"Error: tests directory does not exist: {TESTS_DIR}", file=sys.stderr)
+        return []
+    
+    test_files = []
+    for ext in ['.in', '.out']:
+        test_files.extend(TESTS_DIR.glob(f'*{ext}'))
+    
+    return sorted(test_files)
+
+
+def main():
+    """Main function."""
+    # Parse arguments
+    fix_mode = '--fix' in sys.argv or '-f' in sys.argv
+    verbose = '--verbose' in sys.argv or '-v' in sys.argv
+    
+    # Find all test files
+    test_files = find_test_files()
+    
+    if not test_files:
+        print("No test files found.")
+        return 0
+    
+    if verbose:
+        print(f"Checking {len(test_files)} test files...")
+    
+    # Check files
+    problematic_files = []
+    for file_path in test_files:
+        if check_file(file_path):
+            problematic_files.append(file_path)
+    
+    # Show results
+    if not problematic_files:
+        print("✓ All test files are OK (no double newline endings).")
+        return 0
+    
+    print(f"\nFound {len(problematic_files)} files ending with two newlines:\n")
+    for file_path in problematic_files:
+        rel_path = file_path.relative_to(PROJECT_ROOT)
+        print(f"  {rel_path}")
+    
+    # Fix mode
+    if fix_mode:
+        print(f"\nFixing {len(problematic_files)} files...")
+        fixed_count = 0
+        failed_count = 0
+        
+        for file_path in problematic_files:
+            if fix_file(file_path):
+                fixed_count += 1
+                if verbose:
+                    rel_path = file_path.relative_to(PROJECT_ROOT)
+                    print(f"  ✓ Fixed: {rel_path}")
+            else:
+                failed_count += 1
+                rel_path = file_path.relative_to(PROJECT_ROOT)
+                print(f"  ✗ Fix failed: {rel_path}", file=sys.stderr)
+        
+        print(f"\nFix complete: {fixed_count} succeeded, {failed_count} failed")
+        return 0 if failed_count == 0 else 1
+    else:
+        print("\nTip: Use --fix to automatically fix these issues.")
+        return 1
+
+
+if __name__ == '__main__':
+    sys.exit(main())
+