Add test_argument_required

tests/test_arguments.py

@@ -0,0 +1,12 @@
+from subprocess import CalledProcessError
+import unittest
+
+class FirstTestClass(unittest.TestCase):
+
+  def test_argument_required(self):
+    import subprocess
+    with self.assertRaises(CalledProcessError):
+      subprocess.check_output(['python', 'manga_up'])
+
+if __name__ == '__main__':
+  unittest.main()