The test runs the following query:

runAgg([{$project: {nestedProjectField: 1}}]); 

but it means to run

runAgg([{$project: {[nestedProjectField]: 1}}]); 

so that it makes use of the 'nestedProjectField' variable. 

Once this typo is fixed, we'll also need to adjust the query, since 'nestedProjectField' is currently too nested and the server will reject it.