kevinhongzl opened a new pull request, #66983:
URL: https://github.com/apache/airflow/pull/66983
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## Summary
Previously marking both an upstream task and its downstream mapped tasks as
successful could still fail during expansion. Although the mapped task was
marked successful, we still needed upstream XComs to determine how many task
instances to create. When the upstream task was also marked successful and
therefore did not run, no XCom was produced, so expansion failed. This PR
updates `dag.test()` to handle this scenario.
closes: #61558
## Updated behavior
The behavior is now:
```
upstream (marked success) -> no XCom -> mapped (marked success) -> create 1
successful TI
upstream (executed) -> XCom [n] -> mapped (marked success) -> create n
successful TIs
upstream (marked success) -> no XCom -> mapped (executed) -> fail as before
upstream (executed) -> XCom [n] -> mapped (executed) -> create n
executed TIs
```
In other words, when a mapped task is marked successful:
- if upstream mapping data exists, we use it to create the expected number
of mapped task instances
- if upstream mapping data does not exist because the upstream task was also
marked successful, we create a single successful mapped task
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