test: use assert.throw to test exceptions

The test wasn't checking directly that an assertion was thrown. Instead,
it was checking that spawn did not sucessfully spawn a non-existent
command.

However, the command chosen, dir, exists in GNU coreutils, so it exists
on Linux (though not on BSD derived OS X). The test as written passed on
Linux, even with the TypeError it is supposed to be checking for deleted
from spawn(). It would also pass on Windows if a ls.exe existed.

The approach is unnecessarily obscure, assert.throw() is for asserting
code throws, using it is more clear and works regardless of what
commands do or do not exist.

PR-URL: https://github.com/joyent/node/pull/8454
Reviewed-by: Trevor Norris <trev.norris@gmail.com>

Cherry-picked-from: 2ff29cc7e3

Conflicts:
	test/parallel/test-child-process-spawn-typeerror.js

test/parallel/test-child-process-spawn-typeerror.js

@@ -1,23 +1,14 @@
-var spawn = require('child_process').spawn,
-  assert = require('assert'),
-  windows = (process.platform === 'win32'),
-  cmd = (windows) ? 'rundll32' : 'ls',
-  invalidcmd = 'hopefully_you_dont_have_this_on_your_machine',
-  invalidArgsMsg = /Incorrect value of args option/,
-  invalidOptionsMsg = /options argument must be an object/,
-  errors = 0;
-
-try {
-  // Ensure this throws a TypeError
-  var child = spawn(invalidcmd, 'this is not an array');
-
-  child.on('error', function (err) {
-    errors++;
-  });
-
-} catch (e) {
-  assert.equal(e instanceof TypeError, true);
-}
+var assert = require('assert');
+var child_process = require('child_process');
+var spawn = child_process.spawn;
+var cmd = (process.platform === 'win32') ? 'rundll32' : 'ls';
+var invalidArgsMsg = /Incorrect value of args option/;
+var invalidOptionsMsg = /options argument must be an object/;
+
+// verify that args argument must be an array
+assert.throws(function() {
+  spawn(cmd, 'this is not an array');
+}, TypeError);
 
 // verify that valid argument combinations do not throw
 assert.doesNotThrow(function() {
@@ -57,6 +48,3 @@ assert.throws(function() {
   spawn(cmd, [], 1);
 }, invalidOptionsMsg);
 
-process.on('exit', function() {
-  assert.equal(errors, 0);
-});