Reducing suite duration.
WHY IT IS NECESSARY
Suites grow, and duration determines how often they run.
WHAT PARALLELISM REQUIRES
Tests that are independent Data that does not collide Resources that can be shared or duplicated
WHAT BREAKS UNDER PARALLELISM
Shared test accounts Fixed identifiers Shared database state Tests assuming they are alone
WHAT TO DO ABOUT DATA
Each test creating its own, with unique values.
HOW TO ENSURE UNIQUENESS
Generated identifiers, not fixed ones.
WHAT TO DO ABOUT ACCOUNTS
One per test, or a pool with allocation.
WHAT LEVELS OF PARALLELISM EXIST
Across test files Within a file Across machines
WHAT TO START WITH
File-level parallelism, which is usually safe.
WHAT TO MEASURE
Duration before and after Failure rate before and after
WHY THAT SECOND
Parallelism reveals hidden dependencies as new flakiness.
WHAT TO DO WHEN IT DOES
Fix the dependency, rather than reducing parallelism.
WHAT TO BALANCE
Parallelism against resource contention.
WHAT TO WATCH
Whether the environment under test becomes the bottleneck.
