The test attempts to assert that restarting the catalog will correctly restore any state in the event the operation fails. To do this it starts a background index build (which causes closing the catalog to fail), then calls restartCatalog. However, the test calls restartCatalog after it observes the index build in currentOp, which it turns out is not sufficient. The server code will first register the command in CurOp before marking it as a BackgroundOperation. Thus it's possible for the restartCatalog to succeed as it can come in before the index build marks itself as a BackgroundOperation.