Add data validation on schema evolution test after attribute re-add. (#…

…5399)

After evolving a schema to drop an `int` attribute and re-add it as a
`std::string` type, validate that the attribute's data is now empty.

[sc-60287]

---
TYPE: NO_HISTORY
DESC: Add data validation on schema evolution test after attribute
re-add.

test/src/unit-cppapi-schema-evolution.cc

@@ -881,6 +881,13 @@ TEST_CASE(
       .set_offsets_buffer("a", offsets);
   query_r.submit();
   array_r.close();
+  CHECK(buffer.size() == 0);
+  CHECK_THAT(buffer, Catch::Matchers::Equals(std::string{""}));
+  CHECK(offsets.size() == 10);
+  CHECK_THAT(
+      offsets,
+      Catch::Matchers::Equals(
+          std::vector<uint64_t>{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}));
 
   // Read the original array
   std::vector<int> a_data(10);