Add testing for distributed codec (#217)

* Add tests for NetworkCoalesceExec.

* Add standalone NetworkCoalesceExec test and test with n_tasks > 1.

Author: JSOD11

src/protobuf/distributed_codec.rs

@@ -534,4 +534,79 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn test_roundtrip_single_flight_coalesce() -> datafusion::common::Result<()> {
+        let codec = DistributedCodec;
+        let registry = MemoryFunctionRegistry::new();
+
+        let schema = schema_i32("e");
+        let plan: Arc<dyn ExecutionPlan> = Arc::new(new_network_coalesce_tasks_exec(
+            Partitioning::RoundRobinBatch(3),
+            schema,
+            dummy_stage(),
+        ));
+
+        let mut buf = Vec::new();
+        codec.try_encode(plan.clone(), &mut buf)?;
+
+        let decoded = codec.try_decode(&buf, &[empty_exec()], &registry)?;
+        assert_eq!(repr(&plan), repr(&decoded));
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_roundtrip_isolator_flight_coalesce() -> datafusion::common::Result<()> {
+        let codec = DistributedCodec;
+        let registry = MemoryFunctionRegistry::new();
+
+        let schema = schema_i32("f");
+        let flight = Arc::new(new_network_coalesce_tasks_exec(
+            Partitioning::UnknownPartitioning(1),
+            schema,
+            dummy_stage(),
+        ));
+
+        let plan: Arc<dyn ExecutionPlan> =
+            Arc::new(PartitionIsolatorExec::new_ready(flight.clone(), 1)?);
+
+        let mut buf = Vec::new();
+        codec.try_encode(plan.clone(), &mut buf)?;
+
+        let decoded = codec.try_decode(&buf, &[flight], &registry)?;
+        assert_eq!(repr(&plan), repr(&decoded));
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_roundtrip_isolator_union_coalesce() -> datafusion::common::Result<()> {
+        let codec = DistributedCodec;
+        let registry = MemoryFunctionRegistry::new();
+
+        let schema = schema_i32("g");
+        let left = Arc::new(new_network_coalesce_tasks_exec(
+            Partitioning::RoundRobinBatch(2),
+            schema.clone(),
+            dummy_stage(),
+        ));
+        let right = Arc::new(new_network_coalesce_tasks_exec(
+            Partitioning::RoundRobinBatch(2),
+            schema.clone(),
+            dummy_stage(),
+        ));
+
+        let union = Arc::new(UnionExec::new(vec![left.clone(), right.clone()]));
+        let plan: Arc<dyn ExecutionPlan> =
+            Arc::new(PartitionIsolatorExec::new_ready(union.clone(), 3)?);
+
+        let mut buf = Vec::new();
+        codec.try_encode(plan.clone(), &mut buf)?;
+
+        let decoded = codec.try_decode(&buf, &[union], &registry)?;
+        assert_eq!(repr(&plan), repr(&decoded));
+
+        Ok(())
+    }
 }