Add unit tests

Author: gaohao95

examples/off-surface-eval.py

@@ -810,7 +810,7 @@ def exec_compute_potential_insn_fmm(self, actx: PyOpenCLArrayContext,
 
             return results, timing_data
         else:
-            results = []
+            results = [(o.name, None) for o in insn.outputs]
             return results, timing_data
 
 

pytential/qbx/distributed.py

@@ -376,7 +376,7 @@ def exec_assign(self, actx: PyOpenCLArrayContext, insn, bound_expr, evaluate):
         if self.comm.Get_rank() == 0:
             return super().exec_assign(actx, insn, bound_expr, evaluate)
         else:
-            return {}
+            return [(name, None) for name in insn.names]
 
     def exec_compute_potential_insn(
             self, actx: PyOpenCLArrayContext, insn, bound_expr, evaluate):