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>

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

@@ -19,30 +19,18 @@
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-var spawn = require('child_process').spawn,
-  assert = require('assert'),
-  windows = (process.platform === 'win32'),
-  cmd = (windows) ? 'dir' : 'ls',
-  invalidcmd = (windows) ? 'ls' : 'dir',
-  errors = 0;
+var assert = require('assert');
+var child_process = require('child_process');
+var spawn = child_process.spawn;
+var cmd = (process.platform === 'win32') ? 'dir' : 'ls';
 
-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);
-}
+// verify that args argument must be an array
+assert.throws(function() {
+  spawn(cmd, 'this is not an array');
+}, TypeError);
 
 // verify that args argument is optional
 assert.doesNotThrow(function() {
   spawn(cmd, {});
 });
-
-process.on('exit', function() {
-  assert.equal(errors, 0);
-});