Add (currently failing) test for crystal water parsing for 0.8.x

chempy/tests/test_chemistry.py

@@ -570,3 +570,16 @@ def test_balance_stoichiometry__duplicates():
         underdetermined=None,
     )
     assert bal_Mn_COx == ({"CO": 2}, {"C": 1, "CO2": 1})
+
+
+def test_composition_dot_as_crystal_water_chempy08x():
+    """In Chempy v0.8.x a dot will signify crystal water. But an asterisk '*'
+    or and interpunct (·) is also accepted (and preferred).
+    From Chempy v0.9.x on-wards, only interpunct and asterisk will be
+    interpreted as crystal water delimiters, and a dot will be interpreted
+    as floating point delimiter in fractional stoichiometric coefficients."""
+    assert chempy.Substance.from_formula('Zn(NO3)2·6H2O').composition == {30: 1, 7: 2, 8: 12, 1: 12}
+    assert chempy.Substance.from_formula('Zn(NO3)2*6H2O').composition == {30: 1, 7: 2, 8: 12, 1: 12}
+    # https://docs.pytest.org/en/7.1.x/how-to/capture-warnings.html#ensuring-code-triggers-a-deprecation-warning
+    with pytest.deprecated_call():
+        assert chempy.Substance.from_formula('Zn(NO3)2.6H2O').composition == {30: 1, 7: 2, 8: 12, 1: 12}