code: function assert(expr) {
    if (expr) return;
  
    var stack = callsite();
    var call = stack[1];
    var file = call.getFileName();
    var lineno = call.getLineNumber();
    var src = fs.readFileSync(file, 'utf8');
    var line = src.split('\n')[lineno-1];
    var src = line.match(/assert\((.*)\)/)[1];
  
    var err = new AssertionError({
      message: src,
      stackStartFunction: stack[0].getFunction()
    });
  
    throw err;
  }
docs: Assert the given `expr`.