fix test based on expected behavior for xyz files, remove wrong n ato…

…ms tests, that is being tested for in GMSO test_xyz.py

mbuild/tests/test_xyz.py

@@ -22,23 +22,12 @@ def test_load_no_top(self, ethane):
         #    ele.Elements.H,
         # }
 
-    def test_wrong_n_atoms(self):
-        with pytest.raises(MBuildError):
-            mb.load(get_fn("too_few_atoms.xyz"))
-        with pytest.raises(MBuildError):
-            mb.load(get_fn("too_many_atoms.xyz"))
-
-    def test_bad_input(self, ethane):
-        with pytest.raises(ValueError):
-            assert isinstance(ethane, mb.Compound)
-            write_xyz(ethane, "compound.xyz")
-
     def test_save(self, ethane):
         ethane.save(filename="ethane.xyz")
         ethane_in = mb.load("ethane.xyz")
-        assert len(ethane_in.children) == 8
+        assert len(ethane_in.children) == 1
         assert ethane_in.n_bonds == 0
-        assert set([child.name for child in ethane_in.children]) == {"C", "H"}
+        assert set([p.name for p in ethane_in.particles()]) == {"C", "H"}
 
     def test_coordinates(self, ethane):
         ethane.save(filename="ethane.xyz")