Bug/various (#26)

* disallow bad args

* disallow bad args at Quantity construction

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* disallow bad args at Quantity construction

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/ansys/units/docs/README.rst

@@ -79,7 +79,7 @@ Import the pyunits library:
 
 .. code:: python
 
-   import ansys.untis as q
+   import ansys.units as q
 
 Quantities can be instantiated with 1 of 3 methods:
 

src/ansys/units/quantity.py

@@ -293,3 +293,7 @@ def INCOMPATIBLE_DIMENSIONS(cls, from_unit, to_unit):
     @classmethod
     def INCOMPATIBLE_VALUE(cls, value):
         return cls(f"`{value}` is incompatible with the current quantity object.")
+
+    @classmethod
+    def UNKNOWN_UNITS(cls, unit: str):
+        return cls(f"`{unit}` is an unknown or unconfigured unit.")

src/ansys/units/tables.py

@@ -2,6 +2,8 @@
 
 import yaml
 
+from ansys.units.quantity import Quantity, QuantityError  # noqa: F401
+
 
 class UnitsTable(object):
     """Initializes a UnitsTable object with all table values and unit string
@@ -54,7 +56,7 @@ def _has_multiplier(self, unit_term: str) -> bool:
             Boolean of multiplier within unit_term.
         """
         # Check if the unit term is not an existing fundamental or derived unit.
-        return not (
+        return unit_term and not (
             (unit_term in self._fundamental_units) or (unit_term in self._derived_units)
         )
 
@@ -135,14 +137,20 @@ def filter_unit_term(self, unit_term: str) -> tuple:
         base = unit_term
 
         # strip multiplier and base from unit term
-        if self._has_multiplier(unit_term):
+        has_multiplier = self._has_multiplier(unit_term)
+        if has_multiplier:
             for mult in self._multipliers:
                 if unit_term.startswith(mult):
                     if not self._has_multiplier(unit_term[len(mult) :]):
                         multiplier = mult
                         base = unit_term[len(mult) :]
                         break
 
+        # if we thought it had a multiplier, that's just because the string wasn't
+        # a known unit on its own. So if we can't actually find its multiplier then
+        # this string is an invalid unit string
+        if has_multiplier and not multiplier:
+            raise QuantityError.UNKNOWN_UNITS(unit_term)
         return multiplier, base, power
 
     def si_data(

tests/test_quantity.py

@@ -938,3 +938,12 @@ def test_error_messages():
 
     e3 = q.QuantityError.INCOMPATIBLE_VALUE("radian")
     assert e3.__str__() == "`radian` is incompatible with the current quantity object."
+
+
+def test_instantiate_quantity_with_unrecognized_units_causes_exception():
+    with pytest.raises(q.QuantityError):
+        q.Quantity(value=10, units="piggies")
+    with pytest.raises(q.QuantityError):
+        q.Quantity(value=10, units="piggies s^-1")
+    with pytest.raises(q.QuantityError):
+        q.Quantity(value=10, units="piggies^2 m^-3")