unit testing - How do I test that a specific exception is thrown in node.js and tap -

i use assert(...) on methods validate arguments, e.g.

var assert = require('assert')  function somefunction(a, b, c) {   assert(a, 'a required')   assert(b, 'b required')   assert(c, 'c required') } 

i using tap , write test validate assert exception thrown. cannot test error thrown, because assert early-guard. bad input throw error.

you compare against assert.assertionerror in t.throws() e.g.

var test = require('tap').test  test('calling somefunction without arguments', function(t){   t.throws(function(){     somefunction()   }, new assert.assertionerror({     message: 'a required'   }), 'throws assert error')   t.end() }) 

the assertionerror takes object in it's constructor .message property compared against thrown exception.