test: split independent tests into separate files

Move ENOENT related tests out of general fs.watch() test file and into
its own file. This may help diagnose
#3541.

PR-URL: #3548
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>

test/parallel/test-fs-watch-enoent.js

@@ -0,0 +1,21 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fs = require('fs');
+
+assert.throws(function() {
+  fs.watch('non-existent-file');
+}, function(err) {
+  assert(err);
+  assert(/non-existent-file/.test(err));
+  assert.equal(err.filename, 'non-existent-file');
+  return true;
+});
+
+const watcher = fs.watch(__filename);
+watcher.on('error', common.mustCall(function(err) {
+  assert(err);
+  assert(/non-existent-file/.test(err));
+  assert.equal(err.filename, 'non-existent-file');
+}));
+watcher._handle.onchange(-1, 'ENOENT', 'non-existent-file');

test/sequential/test-fs-watch.js

@@ -126,20 +126,3 @@ assert.throws(function() {
   w.stop();
 }, TypeError);
 oldhandle.stop(); // clean up
-
-assert.throws(function() {
-  fs.watch('non-existent-file');
-}, function(err) {
-  assert(err);
-  assert(/non-existent-file/.test(err));
-  assert.equal(err.filename, 'non-existent-file');
-  return true;
-});
-
-var watcher = fs.watch(__filename);
-watcher.on('error', common.mustCall(function(err) {
-  assert(err);
-  assert(/non-existent-file/.test(err));
-  assert.equal(err.filename, 'non-existent-file');
-}));
-watcher._handle.onchange(-1, 'ENOENT', 'non-existent-file');