tweaks

tests/test_fits_header_ops.py

@@ -132,3 +132,7 @@ class TestFitsHeaderOps(unittest.TestCase):
     def test_generate_meta(self):
         h = generate_meta()
         self.assertIsInstance(h, fits.Header)
+
+    def test_generate_meta_with_invalid_args(self):
+        with self.assertRaises(AssertionError):
+            generate_meta(obs_id=1)