The jstests/aggregation/variables/ directory was introduced in 2f367a1 as part of SERVER-27614. However, the jstests/aggregation/variables/ directory was only added to the "roots" section of the aggregation.yml test suite. This means these tests aren't running in the following test suites:

• aggregation_auth.yml
• aggregation_ese.yml
• aggregation_facet_unwind_passthrough.yml
• aggregation_read_concern_majority_passthrough.yml
• aggregation_sharded_collections_passthrough.yml

I think we should change the "roots" section to jstests/aggregation/**/*.js and specifically exclude the jstests/aggregation/data/ and jstests/aggregation/extras/ directories in order to avoid this kind of situation in the future.