clean up how we check that the process runs... This is better as it

allows to check output, and prevents spamming to test console.  It
also sets up the environment closer to a real run.

ntunnel.py

@@ -316,21 +316,34 @@ class TestMain(unittest.TestCase):
 		shutil.rmtree(self.basetempdir)
 		self.tempdir = None
 
-	def test_noargs(self):
-		sys.argv = [ 'prog' ]
+	@async_test
+	async def test_noargs(self):
+		proc = await self.run_with_args()
 
-		with self.assertRaises(SystemExit) as cm:
-			main()
+		await proc.wait()
 
 		# XXX - not checking error message
 
 		# And that it exited w/ the correct code
-		self.assertEqual(5, cm.exception.code)
+		self.assertEqual(proc.returncode, 5)
+
+	def run_with_args(self, *args):
+		return asyncio.create_subprocess_exec(sys.executable,
+		    __file__, *args,
+		    stdout=asyncio.subprocess.PIPE,
+		    stderr=asyncio.subprocess.PIPE)
 
-	def test_genkey(self):
+	def test_both(self):
+		pass
+
+	@async_test
+	async def test_genkey(self):
 		# that it can generate a key
-		sys.argv = [ 'prog', 'genkey', 'somefile' ]
-		main()
+		proc = await self.run_with_args('genkey', 'somefile')
+
+		await proc.wait()
+
+		self.assertEqual(proc.returncode, 0)
 
 		with open('somefile.pub', encoding='ascii') as fp:
 			lines = fp.readlines()
@@ -347,13 +360,17 @@ class TestMain(unittest.TestCase):
 			self.assertIsInstance(key, x448.X448PrivateKey)
 
 		# that a second call fails
-		with self.assertRaises(SystemExit) as cm:
-			main()
+		proc = await self.run_with_args('genkey', 'somefile')
 
-		# XXX - not checking error message
+		await proc.wait()
+
+		stdoutdata, stderrdata = await proc.communicate()
+
+		self.assertFalse(stdoutdata)
+		self.assertEqual(b'failed to create somefile.pub, file exists.\n', stderrdata)
 
 		# And that it exited w/ the correct code
-		self.assertEqual(1, cm.exception.code)
+		self.assertEqual(proc.returncode, 1)
 
 class TestNoiseFowarder(unittest.TestCase):
 	def setUp(self):