add length-1 case in to combine_uvpspec in response to @adeliegorce '…

…s review

hera_pspec/tests/test_uvpspec.py

@@ -733,6 +733,10 @@ def test_combine_uvpspec(self):
                                          beam=beam)
         uvp1 = self._add_optionals(uvp1)
 
+        # test single UVPSpec
+        out = uvpspec.combine_uvpspec([uvp1], verbose=False)
+        assert id(out) == id(uvp1)
+
         # test concat across pol
         uvp2 = copy.deepcopy(uvp1)
         uvp2.polpair_array[0] = 1414

hera_pspec/uvpspec.py

@@ -2351,6 +2351,10 @@ def combine_uvpspec(uvps, merge_history=True, verbose=True):
     u : UVPSpec object
         A UVPSpec object with the data of all the inputs combined.
     """
+    # Check if only one UVPSpec object is given
+    if (len(uvps) == 1) and issubclass(type(uvps[0]), UVPSpec):
+        return uvps[0]
+
     # Perform type checks and get concatenation axis
     (uvps, concat_ax, new_spws, new_blpts, new_polpairs,
      static_meta) = get_uvp_overlap(uvps, just_meta=False, verbose=verbose)