test: add test case for table scan

Author: wgtmac

src/iceberg/table_scan.cc

@@ -384,6 +384,9 @@ const std::shared_ptr<TableMetadata>& TableScan::metadata() const { return metad
 Result<std::shared_ptr<Snapshot>> TableScan::snapshot() const {
   auto snapshot_id = context_.snapshot_id ? context_.snapshot_id.value()
                                           : metadata_->current_snapshot_id;
+  if (snapshot_id == kInvalidSnapshotId) {
+    return std::shared_ptr<Snapshot>{nullptr};
+  }
   return metadata_->SnapshotById(snapshot_id);
 }
 

src/iceberg/table_scan.h

@@ -275,7 +275,7 @@ class ICEBERG_EXPORT TableScan {
   /// \brief Returns the table metadata being scanned.
   const std::shared_ptr<TableMetadata>& metadata() const;
 
-  /// \brief Returns the snapshot to scan.
+  /// \brief Returns the snapshot to scan. If there is no snapshot, returns nullptr.
   Result<std::shared_ptr<Snapshot>> snapshot() const;
 
   /// \brief Returns the projected schema for the scan.

src/iceberg/test/CMakeLists.txt

@@ -162,7 +162,11 @@ if(ICEBERG_BUILD_BUNDLE)
                    parquet_schema_test.cc
                    parquet_test.cc)
 
-  add_iceberg_test(scan_test USE_BUNDLE SOURCES file_scan_task_test.cc)
+  add_iceberg_test(scan_test
+                   USE_BUNDLE
+                   SOURCES
+                   file_scan_task_test.cc
+                   table_scan_test.cc)
 
   add_iceberg_test(table_update_test
                    USE_BUNDLE