Node assert.throws not catching exception

Question

Given this code:

var assert = require('assert');  function boom(){     throw new Error('BOOM'); }  assert.throws( boom(), Error ); 

I get this output, with node 0.4.9:

node.js:134         throw e; // process.nextTick error, or 'error' event on first tick         ^ Error: BOOM     at boom ([EDITED]/assert.throws.test.js:4:9)     at Object.<anonymous> ([EDITED]/assert.throws.test.js:7:17)     at Module._compile (module.js:402:26)     at Object..js (module.js:408:10)     at Module.load (module.js:334:31)     at Function._load (module.js:293:12)     at Array.<anonymous> (module.js:421:10)     at EventEmitter._tickCallback (node.js:126:26) 

This, to me, implies that an uncaught exception has occurred, as opposed to a reported, caught exception. Looking in the docs, I notice that the examples look more like this:

var assert = require('assert');  function boom(){     throw new Error('BOOM'); }  assert.throws( boom, Error ); 

But how do you test if it throws an exception given a certain input? For example:

var assert = require('assert');  function boom(blowup){     if(blowup)         throw new Error('BOOM'); }  assert.throws( boom, Error ); 

This will fail. What am I doing wrong, or what secret does everybody know but me?

Answer 1

The examples take a function, while your sample code calls a function and passes the result. The exception happens before the assert even gets to look at it.

Change your code to this:

var assert = require('assert');  function boom(){     throw new Error('BOOM'); }  assert.throws( boom, Error ); // note no parentheses 

EDIT: To pass parameters, just make another function. After all, this is javascript!

var assert = require('assert');  function boom(blowup){     if(blowup)         throw new Error('BOOM'); }  assert.throws( function() { boom(true); }, Error ); 

Answer 2

You can use bind():

assert.throws( boom.bind(null), Error ); 

With arguments it is:

assert.throws( boom.bind(null, "This is a blowup"), Error );