Add argument name check in preprocess_and_wrap, and fix dewpoint_from…

…_specific_humidity

src/metpy/calc/thermo.py

@@ -3053,7 +3053,7 @@ def static_stability(pressure, temperature, vertical_dim=0):
 @exporter.export
 @preprocess_and_wrap(
     wrap_like='temperature',
-    broadcast=('pressure', 'temperature', 'specific_humdiity')
+    broadcast=('pressure', 'temperature', 'specific_humidity')
 )
 @check_units('[pressure]', '[temperature]', '[dimensionless]')
 def dewpoint_from_specific_humidity(pressure, temperature, specific_humidity):

src/metpy/xarray.py

@@ -1170,9 +1170,18 @@ def preprocess_and_wrap(broadcast=None, wrap_like=None, match_unit=False, to_mag
         xarray arguments to Quantity, and do not change other array-like arguments.
     """
     def decorator(func):
+        sig = signature(func)
+        if broadcast is not None:
+            for arg_name in broadcast:
+                if arg_name not in sig.parameters:
+                    raise ValueError(
+                        f'Cannot broadcast argument {arg_name} as it is not in function '
+                        'signature'
+                    )
+
         @functools.wraps(func)
         def wrapper(*args, **kwargs):
-            bound_args = signature(func).bind(*args, **kwargs)
+            bound_args = sig.bind(*args, **kwargs)
 
             # Auto-broadcast select xarray arguments, and update bound_args
             if broadcast is not None:

tests/test_xarray.py

@@ -1298,6 +1298,14 @@ def func(a, b):
     assert_array_equal(func(data, data2), [[0, 1, 2], [0, 0, 0], [0, 0, 0]] * units('N m'))
 
 
+def test_preprocess_and_wrap_broadcasting_error():
+    """Test that decorator with bad arguments specified to broadcast errors out."""
+    with pytest.raises(ValueError):
+        @preprocess_and_wrap(broadcast=('a', 'c'))
+        def func(a, b):
+            return a + b
+
+
 def test_preprocess_and_wrap_with_to_magnitude():
     """Test preprocessing and wrapping with casting to magnitude."""
     data = xr.DataArray([1, 0, 1] * units.m)