Refactor TestGrouping.java to break TestRandom into separate tests [LUCENE-5065]

[asfimport]

lucene/grouping/src/test/org/apache/lucene/search/grouping
TestGrouping.java combines multiple tests inside of one test: TestRandom().
This makes it difficult to understand or for new users to use the TestGrouping.java as an entry to understanding grouping functionality.

Either break TestRandom into separate tests or add small separate tests for the most important parts of TestRandom.

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Migrated from LUCENE-5065 by Tom Burton-West, updated Jun 23 2013

[asfimport]

Martijn van Groningen (@martijnvg) (migrated from JIRA)

+1! This test has really become unreadable / unmaintainable.

I would split it into separate test classes each testing a specific part:

• A test that both tests the first and second pass collector.
• Some as above but then a sharded test.
• Move the test for the all groups collector to AllGroupsCollectorTest.
• Move out the block grouping to a dedicated test.
• I think the usage of CacheCollector can be removed and perhaps this can just be tested via the 'GroupingSearchTest' class.

This is a big tasks :-) So it would be a more digestible task if this is done step by step.