BulkImportResponse response = await bulkExecutorWrapper.BulkImport(documents, enableUpsert);
if (response .NumberOfDocumentsImported != documents.Count)
{
   //Do some  logic
}

bulkExecutorWrapper.Setup(bulkExecutorWrapper=> bulkExecutorWrapper.BulkImport(It.IsAny<List<object>>(), It.IsAny<bool>())).ReturnsAsync(new BulkImportResponse(){NumberOfDocumentsImported = 0});