Error serialization must handle non-errors better

[novemberborn]

serialize-error currently does not guard against being called with a null or undefined value.

import test from 'ava'

test.cb(t => {
  setImmediate(() => {throw null})
  setImmediate(t.end)
})

results in:

❯ npx ava

  1 passed
  1 exception

  Uncaught Exception
  Error: Failed to serialize uncaught exception
    at process.on.exception (/private/var/folders/2_/qczp184x76b2nl034sq5hvxw0000gn/T/tmp.dcvW5BUyA5/node_modules/ava/lib/test-worker.js:93:15)
    at emitOne (events.js:115:13)
    at process.emit (events.js:210:7)
    at process._fatalException (bootstrap_node.js:374:26)

Similarly, if a primitive is thrown, the output is terrible:

import test from 'ava'

test.cb(t => {
  setImmediate(() => {throw 5})
  setImmediate(t.end)
})

❯ npx ava

  1 passed
  1 exception

  Uncaught Exception
  Threw non-error: {"avaAssertionError":false,"source":null,"object":5,"type":"exception","file":"test.js"}

The same goes when throwing objects:

import test from 'ava'

test.cb(t => {
  setImmediate(() => {throw new Date()})
  setImmediate(t.end)
})

❯ npx ava

  1 passed
  1 exception

  Uncaught Exception
  Threw non-error: {"avaAssertionError":false,"source":null,"object":{},"type":"exception","file":"test.js"}

If the error doesn't seem to be an error we should format it and print that instead.

[sindresorhus]

WIth:

throw 1;

I would print:

Threw non-error: 1
YOU SHOULD NOT THROW NON-ERRORS. GO THINK ABOUT WHAT YOU DID.

Jokes aside, I'm serious about including the first sentence in some form. People should learn. The fact that it's even allowed in JS is very JS, but also very annoying.

[novemberborn]

Here we're dealing with errors that are not handled in the test or by assertions. They could even be bugs (throw err where err is an undefined variable). I don't think we need to proselytize in the uncaught exception handler. That's what t.throws() is for.

[sindresorhus]

Ok

[novemberborn]

This was fixed in #1722.