Why is only one test running at a time?

Check your concurrency settings first. Extra tests wait as Queued until a free slot is available. That often looks like only one test is running.

1. Open Settings > Runners and find Concurrency Limits.
2. For each concurrency control on the page, choose Fastest Runs, or raise the slider if you keep Limit Concurrency. Press Save.
3. Open the Flow settings and check Run in isolation. When this is on, that Flow's tests run one after another.
4. Start a new Run after you change the settings. An in-progress Run, and a rerun of an older Run, keep the concurrency settings they started with.
5. For CI/CD Runs, check whether the pipeline sets a concurrency value for the Run, and raise or remove it.

If every concurrency control is set to Fastest Runs, the Flow is not set to run in isolation, and a new Run still starts tests one at a time, open Help in DoesQA and select Create new ticket. Include the Run ID.