The struct MockMongoInterface defined in /home/ubuntu/mongo-dev/mongo/src/mongo/db/pipeline/change_stream_stage_test_fixture.h has the potential to create conflict with classes with identical names defined in a number of other files, for example 

/home/ubuntu/mongo-dev/mongo/src/mongo/db/pipeline/document_source_find_and_modify_image_lookup_test.cpp

/home/ubuntu/mongo-dev/mongo/src/mongo/db/pipeline/search/document_source_list_search_indexes_test.cpp

/home/ubuntu/mongo-dev/mongo/src/mongo/db/s/resharding/resharding_agg_test.cpp

...

Rename the struct name used in the change_stream_stage_test_fixture.h header file to avoid conflicting definitions if the header file is included in one of the above source files.