How one dev team cut redundant CI runs in a merge queue to speed up delivery

A software development team found that their merge queue, adopted to speed up code delivery, was running a full test suite separately for each pull request waiting to land — meaning four queued PRs triggered four complete runs, even though the last already included the others. Their test suite comprised over 15,000 tests taking 13 to 19 minutes per run, with 93% of CI time consumed by the test step alone. The team discovered that the slowest 1% of tests — around 226 that spin up real processes and migrate databases — accounted for 41% of total test time, making simple test deletion ineffective. After moving compute to idle owned hardware, the same suite dropped from up to 16 minutes to 108 seconds. The article examines whether redundant runs in a merge queue can be safely eliminated and what approaches to stopping them are viable.