Add debug print to flaky JSON test (#2404)

Initialize all members to avoid undefined values.

arbor/backends/gpu/shared_state.hpp

@@ -143,9 +143,9 @@ struct ARB_ARBOR_API shared_state: shared_state_base<shared_state, array, ion_st
     arb_size_type n_cv = 0;       // Total number of CVs.
 
     iarray cv_to_cell;            // Maps CV index to cell index.
-    arb_value_type time;          // integration start time [ms].
-    arb_value_type time_to;       // integration end time [ms]
-    arb_value_type dt;            // dt [ms].
+    arb_value_type time = 0.0;    // integration start time [ms].
+    arb_value_type time_to = 0.0; // integration end time [ms]
+    arb_value_type dt  = 0.0;     // dt [ms].
     array voltage;                // Maps CV index to membrane voltage [mV].
     array current_density;        // Maps CV index to current density [A/m²].
     array conductivity;           // Maps CV index to membrane conductivity [kS/m²].

arbor/backends/multicore/shared_state.hpp

@@ -152,9 +152,9 @@ struct ARB_ARBOR_API shared_state:
     arb_size_type n_cv = 0;         // Total number of CVs.
 
     iarray cv_to_cell;              // Maps CV index to GID
-    arb_value_type time;            // integration start time [ms].
-    arb_value_type time_to;         // integration end time [ms]
-    arb_value_type dt;              // dt [ms].
+    arb_value_type time = 0.0;      // integration start time [ms].
+    arb_value_type time_to = 0.0;   // integration end time [ms]
+    arb_value_type dt = 0.0;        // dt [ms].
     array voltage;                  // Maps CV index to membrane voltage [mV].
     array current_density;          // Maps CV index to membrane current density contributions [A/m²].
     array conductivity;             // Maps CV index to membrane conductivity [kS/m²].

python/test/unit/test_io.py

@@ -246,4 +246,8 @@ def test_serialize(self):
         rec = serdes_recipe()
         sim = A.simulation(rec)
         jsn = sim.serialize()
-        sim.deserialize(jsn)
+        try:
+            sim.deserialize(jsn)
+        except RuntimeError as e:
+            print(f"Unexpected error\n{e}\nin JSON:\n{jsn}")
+            raise