Add more tests for selection I/O.

src/H5Dscatgath.c

@@ -718,7 +718,7 @@ H5D__scatgath_write(const H5D_io_info_t *io_info, const H5D_dset_io_info_t *dset
             /* Use "vp" field of union to twiddle away const.  OK because if we're doing this it means the
              * user explicitly allowed us to modify this buffer via H5Pset_modify_write_buf(). */
             tmp_buf = (uint8_t *)dset_info->buf.vp + dset_info->layout_io_info.contig_piece_info->buf_off +
-                      (smine_start * dset_info->type_info.dst_type_size);
+                      (smine_start * dset_info->type_info.src_type_size);
         }
         else {
             /* Do type conversion using intermediate buffer */