fix bad json error

Author: paleolimbot

src/nanoarrow/nanoarrow_testing.hpp

@@ -714,7 +714,8 @@ class TestingJSONReader {
       ArrowArrayStreamMove(stream.get(), out);
       return NANOARROW_OK;
     } catch (json::exception& e) {
-      ArrowErrorSet(error, "Exception in TestingJSONReader::ReadBatch(): %s", e.what());
+      ArrowErrorSet(error, "Exception in TestingJSONReader::ReadDataFile(): %s",
+                    e.what());
       return EINVAL;
     }
   }

src/nanoarrow/nanoarrow_testing_test.cc

@@ -774,6 +774,9 @@ TEST(NanoarrowTestingTest, NanoarrowTestingTestRoundtripDataFile) {
   std::stringstream data_file_json_roundtrip;
   ASSERT_EQ(writer.WriteDataFile(data_file_json_roundtrip, stream.get()), NANOARROW_OK);
   EXPECT_EQ(data_file_json_roundtrip.str(), data_file_json);
+
+  // Also test error for invalid JSON
+  ASSERT_EQ(reader.ReadDataFile("{", stream.get()), EINVAL);
 }
 
 TEST(NanoarrowTestingTest, NanoarrowTestingTestReadBatch) {