I wonder the API's just simple description, like the API assert.fail<http://nodemanual.org/0.8.14/nodejs_ref_guide/assert.html#assert.fail>,
when I follow the example code, I can not get the correct output as the
comment say:

-- Code --

var assert = require('assert');

var iX = 4;
var iY = 5;

assert.fail(iX, iY, "iX is bigger than iY", "<");
// prints nothing, because it does not fail

assert.fail(iX, iY, "iX is bigger than iY", ">");
// prints a failure, because iX > iY is not true

-- Code end --

The following is the API description:

So, Throws an exception that displays the values for actual and expected separated