[Integration] Add integration tests for Union types

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Reporter: Wes McKinney / @wesm
Assignee: Antoine Pitrou / @pitrou

Related issues:

• [Python, Java] UnionArray round trip not working (blocks)
• [C++] Complete round trip Union file/stream IPC tests (is blocked by)
• Completing integration tests for major implemented data types (is a parent of)
• [JAVA] Restructure ValueVector hierarchy to minimize compile-time generated code (relates to)

PRs and other links:

• GitHub Pull Request #6948

_{Note: This issue was originally created as ARROW-590. Please see the migration documentation for further details.}

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Li Jin / @icexelloss:
PR: #987

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Wes McKinney / @wesm:
I think this is going to miss 0.7.0 while ARROW-1463 is in discussion

cc @siddharthteotia

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Wes McKinney / @wesm:
Moving this to 0.9.0 as ARROW-1463 is the priority for this release

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Wes McKinney / @wesm:
I doubt this will be resolved for 0.13 (timeline: end of March).

@pravindra now that there are more active Dremio developers in Apache Arrow can you offer some assistance with the ongoing discussion about unions and integration testing for them?

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Pindikura Ravindra / @pravindra:
@wesm, will do.Will work on this next week.

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Ben Kietzman / @bkietz:
Issue resolved by pull request 6948
#6948