Currently, QueryTester will optimize dropping and loading collections across sequential files that use the same underlying collection. This requires the test files to be passed in with one mongotest invocation. However, resmoke will only process one test file at a time, so it won't be possible to pass multiple files into -t from a resmoke invocation. To address this issue, we should allow QueryTester to optimize dropping and loading collections across multiple resmoke invocations. We can use listCollections with a filter on the collection name to check if a collection is already loaded in the mongod.