Asserting a range with descriptive error messages

Node.js Version

v22

NPM Version

10.8.2

Operating System

MacOS Sonoma

Subsystem

assert

Description

I work a lot with performance testing code which frequently leads in the unfortunate position where I need to assert ranges rather than exact values, i.e

is value between 1500 and 2000?

Now, to do that I use a pair of assert.ok like so:

const value = 1700

assert.ok(value >= 1500)
assert.ok(value <= 2000)

so far so good, could be better but that's clean and concise enough for my taste.

The problem is that setting a descriptive error message quickly becomes rather repetitive and convoluted.

I have to resort to something akin to this:

assert.ok(value >= 1500, `expected value >= 1500 , got: ${value}`)
assert.ok(value <= 2000, `expected value <= 2000 , got: ${value}`)

Apart from cooking up my own assertion functions, is there a better way to do this out-the-box that I'm missing?

CC @nodejs/assert

looks reasonable to me!

@nicholaswmin

@nicholaswmin - pls feel free to raise a PR if you are willing to!

Although, doesn't the assert message include the failed assertion line, so wouldn't it already show the failure?

@redyetidev here's the output:

import test from 'node:test'

await test('is within range',  async t => {
  const value = 2700
  
  t.assert.ok(value >= 1500)
  t.assert.ok(value <= 2000)
})

✖ is within range (1.220792ms)
  AssertionError [ERR_ASSERTION]: false == true
      at assert.<computed> [as ok] (node:internal/test_runner/test:261:18)
      at TestContext.<anonymous> (file:///Users/nicholaswmin/Projects/fsm/scratch.js:7:12)
      at Test.runInAsyncScope (node:async_hooks:211:14)
      at Test.run (node:internal/test_runner/test:878:25)
      at Test.processPendingSubtests (node:internal/test_runner/test:590:18)
      at node:internal/test_runner/harness:252:20
      at node:internal/process/task_queues:151:7
      at AsyncResource.runInAsyncScope (node:async_hooks:211:14)
      at AsyncResource.runMicrotask (node:internal/process/task_queues:148:8) {
    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: false,
    expected: true,
    operator: '=='
  }

My "complaint" is that it doesn't print value being asserted against, unless I specifically code it to so with that string interpolation.

Now granted, the above is impossible to do with the code I'm providing because that's a Boolean expression.
An ideal API might be something like:

  t.assert.ok(value <= 2000, value)
  t.assert.ok(value <= 2000, value)

AssertionError [ERR_ASSERTION]: Failed, value: 2700 was not ok

Hmm.. I'm a bit confused... Not sure why I opened this issue as what I'm proposing sounds like a silly API.

Doing this:

t.assert.ok(value <= 2000, value)

prints the value anyway.

I don't remember what I had in mind. Sorry.

assert.isGreaterThan (and vise versa) could work if you'd like to add it?

I'm personally against adding specific assertion checks to assert like that.

It'll eventually snowball into a myriad utilities. I miss the hyper-declarative syntax of Chai but I've also come to love the minimal, no-frills API surface of assert since I don't need to memorise a million method names.

... I don't remember what i had in mind when i opened this.

If I need range checks I can extend assert locally.

I think this needs to be closed ??

The closest thing I can figure out that would help without adding specific assertion checks is printing the expression itself on assert.ok().

An example:

import test from 'node:test'

await test('foo', async t => {
  const value = 2700
  
  t.assert.ok(value >= 1500)
  t.assert.ok(value <= 2000)
})

logs:

✖ is in range (1.220875ms)
  AssertionError [ERR_ASSERTION]: `value >= 1500`
      at assert.<computed> [as ok] (node:internal/test_runner/test:261:18)
      at TestContext.<anonymous> (file:///Users/nicholaswmin/Projects/fsm/scratch.js:7:12)
      at Test.runInAsyncScope (node:async_hooks:211:14)
      at Test.run (node:internal/test_runner/test:878:25)
      at Test.processPendingSubtests (node:internal/test_runner/test:590:18)
      at node:internal/test_runner/harness:252:20
      at node:internal/process/task_queues:151:7
      at AsyncResource.runInAsyncScope (node:async_hooks:211:14)
      at AsyncResource.runMicrotask (node:internal/process/task_queues:148:8) {
    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: false,
    expected: true,
    operator: '=='
  }

which is more descriptive than the current:

AssertionError [ERR_ASSERTION]: false == true

Not sure if that's doable without doing esprima-like parsing though?

For your specific case, a custom error (E.G. throw new assert.AssertionError({actual: 1, expected:2, operator:">="})) can be thrown.

Not sure if that's doable without doing esprima-like parsing though?

In some cases, that is what happens:

import assert from 'node:assert';

assert.ok(25 > 50);

node:internal/modules/run_main:123
    triggerUncaughtException(
    ^

AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:

  assert.ok(25 > 50)

    at file:///Users/avivkeller/Documents/tmp/repro.mjs:3:8
    at ModuleJob.run (node:internal/modules/esm/module_job:262:25)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:482:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:117:5) {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

Node.js v22.8.0

In some cases, that is what happens:

Yes. That works! That's more than enough.

I can repro your working example with assert but not with t.assert

I'm aware. I'm opening an issue for it as we speak.

Fixed in nodejs/node#54776

Amazing;

sorry, life got in the way ...

test_runner: reimplement `assert.ok` to allow stack parsing

@nicholaswmin

@nicholaswmin - is your proposal addressed? can this be closed now as resolved?

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Asserting a range with descriptive error messages #4461

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Asserting a range with descriptive error messages #4461

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avivkeller commented on Aug 4, 2024

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