test: refactor test-fs-buffer

[Trott]

• Remove unneeded temp dir cleanup
• Add check for error in .close() callback
• Improve error reporting

On that last bullet point, the previous version of the test reported
errors like this:

AssertionError: [ '.empty-repl-history-file',
  '.node_repl_history',
  'GH-1899-output.js',
  'GH-892-request.js',
  'a.js',
  'a1.js',
  'agen deepStrictEqual [ '.empty-repl-history-file',
  '.node_repl_history',
  'GH-1899-output.js',
  'GH-892-request.js',
  'a.js',
  'a1.js',
  'agen

Now, they look like this:

AssertionError: 2a is hex value for * and not catch-stdout-error.js

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

test fs

[joyeecheung]

I think the more common wording would be something like

const valHex = Buffer.from(val).toString('hex');
const message = `expected ${valHex} as hex value for ${val}, ` +
                `got ${hexList[idx]} (hex value for ${fromHexList})`

If I am reading this correctly?

[Trott]

Your wording is better. Will update...

[Trott]

How about this?:

`expected ${val}, got ${fromHexList} by hex decoding ${hexList[idx]}`

The thing I'm trying to convey is this: val is the input. We put it in a file hex encoded. We read the file back in and got the hex-encoded value hexList[idx]. When we hex decode that value, we got fromHexList instead of val.

[joyeecheung]

Yeah your proposal works too, and it is more succinct :)

[Trott]

CI: https://ci.nodejs.org/job/node-test-pull-request/6316/

[Trott]

Landed in 05be623

[jasnell]

would need backport PRs to land in v4 or v6