refactor: Move tests to core/tests

Author: Weijun-H

datafusion/core/src/physical_optimizer/limited_distinct_aggregation.rs

@@ -196,11 +196,11 @@ mod tests {
     use crate::physical_optimizer::enforce_distribution::tests::{
         parquet_exec_with_sort, schema, trim_plan_display,
     };
-    use crate::physical_optimizer::tests::aggregate_statistics::tests::TestAggregate;
     use crate::physical_plan::aggregates::PhysicalGroupBy;
     use crate::physical_plan::collect;
     use crate::physical_plan::memory::MemoryExec;
     use crate::prelude::SessionContext;
+    use crate::test_util::TestAggregate;
 
     use arrow::array::Int32Array;
     use arrow::compute::SortOptions;

datafusion/core/src/physical_optimizer/mod.rs

@@ -21,9 +21,6 @@
 //! "Repartition" or "Sortedness"
 //!
 //! [`ExecutionPlan`]: crate::physical_plan::ExecutionPlan
-mod tests {
-    pub mod aggregate_statistics;
-}
 pub mod coalesce_batches;
 pub mod combine_partial_final_agg;
 pub mod enforce_distribution;