add a limit and a test to FlattenExceptionTest.
bug #13004 add a limit and a test to FlattenExceptionTest. (Daniel Wehner)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #13004).

Discussion
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add a limit and a test to FlattenExceptionTest.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #13003
| License       | MIT
| Doc PR        |

Commits
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c6bcf05 add a limit and a test to FlattenExceptionTest.