Unable to compose power-assert + espower in vanilla node 7 or 8

I am trying to use power-assert to get pretty assert output in node, without using mocha or babel.

I’m trying to implement assertions by reading the documentation, but haven’t been able to get it working so far.

Here is my attempt at a “vanilla node” (no mocha) seed: https://github.com/TehShrike/power-assert-espower-repro

entry point:

require('espower-loader')({
	pattern: 'test/*.js',
})

require('./test/test.js')

test/test.js:

const assert = require('power-assert')

const test = () => {
	const value1 = true
	const value2 = 3
	assert.deepEqual({ value: value1 }, { value: value2 })
}

test()

Instead of a nice pretty error message, I get:

/Users/josh/code/power-assert-espower-repro/node_modules/empower-core/lib/decorator.js:110
        ret = func.apply(thisObj, args);
                   ^
AssertionError: { value: true } deepEqual { value: 3 }
    at Decorator._callFunc (/Users/josh/code/power-assert-espower-repro/node_modules/empower-core/lib/decorator.js:110:20)
(snip)

What am I missing? I’m guessing this is a documentation/implementation issue, and not an actual bug.

(node 7.6.0)

[azu]

I’ve figured out this.

// MIT © 2017 azu
const assert = require("assert");
try {
    assert(false);
} catch (e) {
    e.message = "custom message";
    throw e;
}

Node.js 6

/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:7
    throw e;
    ^
AssertionError: custom message
    at Object.<anonymous> (/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:4:5)
    at Module._compile (module.js:556:32)
    at Object.Module._extensions..js (module.js:565:10)
    at Module.load (module.js:473:32)
    at tryModuleLoad (module.js:432:12)
    at Function.Module._load (module.js:424:3)
    at Module.runMain (module.js:590:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:509:3

Node.js 7

/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:7
    throw e;
    ^
AssertionError: false == true
    at Object.<anonymous> (/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:4:5)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)
    at Module.runMain (module.js:605:10)
    at run (bootstrap_node.js:420:7)
    at startup (bootstrap_node.js:139:9)
    at bootstrap_node.js:535:3

Node.js 8:

(Error code is added: https://github.com/nodejs/node/pull/12651)

/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:7
    throw e;
    ^

AssertionError [ERR_ASSERTION]: false == true
    at Object.<anonymous> (/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:4:5)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)
    at Function.Module._load (module.js:458:3)
    at Function.Module.runMain (module.js:605:10)
    at startup (bootstrap_node.js:158:16)
    at bootstrap_node.js:575:3

---

Actually, empower does e.message = buildPowerAssertText(formatter, errorEvent.originalMessage, errorEvent.powerAssertContext);.

• https://github.com/power-assert-js/empower/blob/a4736648889b641cbb85cb2820df1a9ec8f5c5f6/index.js#L44

But, Node.js 7~ does not show this e.message of throwing AssertionError.

I think that Node.js 7~ treat AssertionError as special object.

try {
    throw new Error("!");
} catch (e) {
    e.message = "custom message";
    throw e;
}

Node 8 work fine.

✈ node assert-error.js
/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:7
    throw e;
    ^

Error: custom message
    at Object.<anonymous> (/Users/azu/.ghq/github.com/TehShrike/power-assert-espower-repro/assert-error.js:4:11)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)
    at Function.Module._load (module.js:458:3)
    at Function.Module.runMain (module.js:605:10)
    at startup (bootstrap_node.js:158:16)
    at bootstrap_node.js:575:3

[TehShrike]

After updating the dependencies in my power-assert-espower-repro repository (and removing the duplicate log/throw), this is the output using node 8:

> power-assert-espower-repro@1.0.0 test /Users/josh/code/power-assert-espower-repro
> node index.js

AssertionError [ERR_ASSERTION]:   # test/test.js:6
  
  assert.deepEqual({ value: value1 }, { value: value2 })
                   |        |         |        |        
                   |        |         |        3        
                   |        true      Object{value:3}   
                   Object{value:true}