incorrect/unexpected behavior in assert module

[ORESoftware]

On MacOS 64bit, Node.js version 6.7.0

using the core "assert" module, like so:

  assert.throws(function () {
            const [a, b, c, d] = foo('oh yes');
        }, 
        /Argument is required at argument index = 1, but type was wrong/,
        'did not throw with expected message');

the above is fine, no error is thrown because the block does throw an error with a message that matches the regex

however, if I do this, I get something unexpected (I changed the regex):

 assert.throws(function () {                                                //block arg
            const [a, b, c, d] = foo('oh yes');   
        },
        /Argument is required at argument index = 2, but type was wrong/,  //error arg
        'did not throw with expected message');                            //message arg

it will give me this:

Error: Argument is required at argument index = 1, but type was wrong 
     => expected => "object"
     => actual => "undefined"
        at Object.parse (/Users/t_millal/WebstormProjects/oresoftware/pragmatik/index.js:250:19)
        at foo (/Users/t_millal/WebstormProjects/oresoftware/pragmatik/test/test-src/parse-to-array/three.test.js:31:26)
        at /Users/t_millal/WebstormProjects/oresoftware/pragmatik/test/test-src/parse-to-array/three.test.js:46:34

this is my own library that I am testing, so I am familiar with what is happening. Seems clear that the above error message should at least contain: " 'did not throw with expected message' ". The expected assert module behavior will help me in this regard, but it's not behaving.

Is this a known problem? What am I missing?

[cjihrig]

According to the docs, the third argument is only used if no error is thrown. I think in your case, an error is thrown, but with the wrong message.

[Trott]

Implementing testing-specific assertions like assert.throws() is regarded by many in core to have been a mistake. We're stuck with it because so much of the ecosystem depends on it. But there is mild language in the docs discouraging people from using assert as a general purpose testing library. You might consider using something like chai instead. Their assert API is like the internal module, but likely contains fewer surprises like this. Good luck.