import pytest

from poliastro.bodies import Sun
from poliastro.twobody.mean_elements import get_mean_elements


def test_get_mean_elements_raises_error_if_invalid_body():
    body = Sun

    with pytest.raises(ValueError) as excinfo:
        get_mean_elements(body)
    assert f"The input body '{body}' is invalid." in excinfo.exconly()

import pytest

from poliastro.twobody.mean_elements import get_mean_elements


def test_get_mean_elements_raises_error_if_invalid_body():
    body = "PlanetNine"

    with pytest.raises(ValueError) as excinfo:
        get_mean_elements(body)
    assert f"The input body '{body}' is invalid." in excinfo.exconly()

--- 
+++ 
@@ -1,10 +1,11 @@
 import pytest
 
+from poliastro.bodies import Sun
 from poliastro.twobody.mean_elements import get_mean_elements
 
 
 def test_get_mean_elements_raises_error_if_invalid_body():
-    body = "PlanetNine"
+    body = Sun
 
     with pytest.raises(ValueError) as excinfo:
         get_mean_elements(body)
Add test for error check
