Add unit tests for the outputaccumulator post processing. #808

Job	Run time
Test 'stable' on macos-13 / Unit tests [macos-13]	7m 50s
Test 'stable' on ubuntu-latest / Unit tests [ubuntu-latest]	6m 18s
Test 'stable' on macos-13 / Unit tests [macos-13]	10m 3s
Test 'stable' on macos-13 / Unit tests [macos-13]	6m 45s
Test 'stable' on ubuntu-latest / Unit tests [ubuntu-latest]	6m 22s
Test 'stable' on ubuntu-latest / Unit tests [ubuntu-latest]	7m 33s
Test 'stable' on windows-latest / Unit tests [windows-latest]	16m 22s
Test 'stable' on windows-latest / Unit tests [windows-latest]	11m 47s
Test 'loose' on macos-13 / Unit tests [macos-13]	9m 48s
Test 'loose' on macos-13 / Unit tests [macos-13]	7m 21s
Test 'loose' on macos-13 / Unit tests [macos-13]	7m 49s
Test 'loose' on ubuntu-latest / Unit tests [ubuntu-latest]	6m 43s
Test 'loose' on ubuntu-latest / Unit tests [ubuntu-latest]	6m 48s
Test 'loose' on ubuntu-latest / Unit tests [ubuntu-latest]	6m 39s
Test 'loose' on windows-latest / Unit tests [windows-latest]	14m 54s
Test 'loose' on windows-latest / Unit tests [windows-latest]	14m 12s
Test 'loose' on windows-latest / Unit tests [windows-latest]	19m 4s
Test 'stable' on windows-latest / Unit tests [windows-latest]	15m 2s
	3h 1m 20s

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