Fix the verbose tests

[ehmicky]

The verbose tests are currently randomly failing.

execa/test/verbose.js

Lines 10 to 22 in 5b1a1c7

	test('Prints command when "verbose" is true', async t => {
	const {stdout, stderr, all} = await execa('nested.js', [JSON.stringify({verbose: true}), 'noop.js', 'test'], {all: true});
	t.is(stdout, 'test');
	t.is(normalizeTimestamp(stderr), `${testTimestamp} noop.js test`);
	t.is(normalizeTimestamp(all), `${testTimestamp} noop.js test\ntest`);
	});
	test('Prints command with NODE_DEBUG=execa', async t => {
	const {stdout, stderr, all} = await execa('nested.js', [JSON.stringify({}), 'noop.js', 'test'], {all: true, env: {NODE_DEBUG: 'execa'}});
	t.is(stdout, 'test');
	t.is(normalizeTimestamp(stderr), `${testTimestamp} noop.js test`);
	t.is(normalizeTimestamp(all), `${testTimestamp} noop.js test\ntest`);
	});

  verbose › Prints command when "verbose" is true

  test/verbose.js:14

   13:   t.is(normalizeTimestamp(stderr), `${testTimestamp} noop.js test`);   
   14:   t.is(normalizeTimestamp(all), `${testTimestamp} noop.js test\ntest`);
   15: });                                                                    

  Difference (- actual, + expected):

  - `test␊
  - [00:00:00.000] noop.js test`
  + `[00:00:00.000] noop.js test␊
  + test`

  › file://test/verbose.js:14:4

  verbose › Prints command with NODE_DEBUG=execa

  test/verbose.js:21

   20:   t.is(normalizeTimestamp(stderr), `${testTimestamp} noop.js test`);   
   21:   t.is(normalizeTimestamp(all), `${testTimestamp} noop.js test\ntest`);
   22: });                                                                    

  Difference (- actual, + expected):

  - `test␊
  - [00:00:00.000] noop.js test`
  + `[00:00:00.000] noop.js test␊
  + test`

  › file://test/verbose.js:21:4

This is because the verbose option prints to stderr. When the process prints to stdout, it might be printed first, even if the call to stderr was made before. This is a race condition.

[ehmicky]

Fixed by #600.