tick-to-tree fails with an empty buffer when `tap` measures coverage on Node 8

[AlanSl]

To replicate, on Node 8 (tested on 8.11 and 8.12):

cd 0x

TAP_SNAPSHOT=1 tap test/ticks-to-tree.test.js
# test passes

TAP_SNAPSHOT=1 tap --lines 1 test/ticks-to-tree.test.js
# test fails due to stackChild.stdout being an empty buffer, failing the assert in ticks-to-tree.js 

The same thing happens if a dependent of 0x runs tests that call 0x's ticks-to-tree in a tap test called using any coverage measure.

Obviously this doesn't affect users' usage of 0x. It's just is a problem for 3rd party applications that use 0x and use tap with coverage checks in their CI.

[mcollina]

That's what happening:

Error [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension: /Users/matteo/.node-spawn-wrap-98539-8640f35b202e/node
    at Loader.exports.resolve [as resolver] (internal/loader/ModuleRequest.js:135:13)
    at Loader.resolve (internal/loader/Loader.js:82:40)
    at Loader.getModuleJob (internal/loader/Loader.js:112:40)
    at Loader.import (internal/loader/Loader.js:139:28)
    at module.js:466:29
    at Function.Module._load (module.js:467:7)
    at Function.Module.runMain (module.js:694:10)
    at startup (bootstrap_node.js:204:16)
    at bootstrap_node.js:625:3

[mcollina]

Unfortunately this looks like hard to fix, as it's a bug in spawn-wrap and it uses private core process.bindings that have likely changed between Node.js versions.

[AlanSl]

Maybe it's best then if 3rd parties using 0x simply do their test coverage checks in Node 10 or Node 6, and not Node 8.

Not sure if it's worth including a warning like this (maybe it should be general to spawn wrap rather than specific to tap):

if (process.env._TAP_COVERAGE_ && process.version.match(/^v8\./)) {
  console.warn('Tap coverage checks in Node 8 cause 0x to fail. Please use Node 6 or Node 10, and not Node 8, when calculating test coverage')
}

[mcollina]

IMHO spawn-wrap needs a fix for this.

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