`t.throws` passes with false, undefined, and null

[awmottaz]

Description

t.throws() will pass if provided the arguments false, undefined and null. I would expect these tests to fail since, according to the docs:

error can be an error constructor, error message, regex matched against the error message, or validation function.

For my particular use case, I wanted to test that the error thrown was an instance of a custom error. However, the custom error was not implemented and so undefined was passed into t.throws(). The test still succeeded, which is not the desired behavior.

Test Source

The following tests will incorrectly pass

test('false', t => {
  t.throws(() => { throw new Error('foo') }, false)
})

test('undefined', t => {
  t.throws(() => { throw new Error('foo') }, undefined)
})

test('null', t => {
  t.throws(() => { throw new Error('foo') }, null)
})

Error Message & Stack Trace

▶ node_modules/.bin/ava -v

  ✔ false
  ✔ undefined
  ✔ null

  3 tests passed

Config

Using vanilla ava—no config

Command-Line Arguments

ava -v

Environment

▶ node -e "var os=require('os');console.log('Node.js ' + process.version + '\n' + os.platform() + ' ' + os.release())"
Node.js v8.9.4
linux 4.13.0-32-generic

▶ node_modules/.bin/ava --version
0.25.0

▶ npm --version
5.6.0

[novemberborn]

Yea it should have complained about those arguments. Yet another reason we need to refactor it: #1047.

[novemberborn]

I think we'll have to leave null as an allowable value. It's impossible to specify an assertion message otherwise:

t.throws(fn, null, 'shown when assertion fails')

But as part of #1047 I'll be introducing a more explicit way of defining constructor expectations.