import sys
import traceback
import time
import io

def run_code_against_tests(user_code, test_code):
    import tempfile
    import subprocess
    local_ns = {}
    output = ''
    start = time.perf_counter()
    error = None
    passed = False
    try:
        # Check if unittest is used in test_code
        if 'unittest' in test_code:
            # Write user code + test code to a temp file
            with tempfile.NamedTemporaryFile('w+', suffix='.py', delete=False) as f:
                f.write(user_code + '\n' + test_code)
                f.flush()
                f_name = f.name
            # Run the file as a subprocess
            proc = subprocess.run([sys.executable, f_name], capture_output=True, text=True, timeout=10)
            output = proc.stdout + proc.stderr
            passed = proc.returncode == 0
            error = None if passed else output
        else:
            # Capture stdout
            old_stdout = sys.stdout
            sys.stdout = mystdout = io.StringIO()
            # Execute user code
            exec(user_code, {}, local_ns)
            # Execute test code (should raise AssertionError if fail)
            exec(test_code, local_ns, local_ns)
            passed = True
    except Exception as e:
        passed = False
        error = traceback.format_exc()
    finally:
        if 'mystdout' in locals():
            output = mystdout.getvalue() or output
        sys.stdout = old_stdout if 'old_stdout' in locals() else sys.stdout
    runtime = time.perf_counter() - start
    result = {
        'passed': passed,
        'output': output,
        'runtime': runtime,
        'error': error if not passed else None
    }
    return result