Check attributes for GEBCO and GEBCOSI datasets

pygmt/tests/test_datasets_earth_relief.py

@@ -48,6 +48,10 @@ def test_earth_relief_01d_gebco(data_source):
     data.
     """
     data = load_earth_relief(resolution="01d", data_source=data_source)
+    assert data.attrs["units"] == "meters"
+    assert data.attrs["long_name"] == "Earth elevation relative to the geoid"
+    assert data.attrs["vertical_datum"] == "EGM96"
+    assert data.attrs["horizontal_datum"] == "WGS84"
     assert data.shape == (181, 361)
     assert data.gmt.registration == 0
     npt.assert_allclose(data.lat, np.arange(-90, 91, 1))