added unit test for exiting when no arguments are used except 'orthos…

…nap'

tests/unit/test_parser.py

@@ -39,3 +39,7 @@ def test_support(self, parser):
         assert parsed.fasta == fasta
         assert parsed.tree == tree
         assert parsed.support == float(support)
+
+    def test_parser_when_no_args(self, parser):
+        with pytest.raises(SystemExit):
+            parser.parse_args([])