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The test checks that after different type of GC unreachable objects behave as expected:

1. Young GC - weakly referenced non-humongous objects are collected, other objects are not collected.

2. Full GC - weakly referenced non-humongous and humongous objects are collected, softly referenced non-humongous and
             humongous objects are not collected.

3. Full GC with memory pressure - weakly and softly referenced non-humongous and humongous objects are collected.

4. CMC -  weakly referenced non-humongous objects are collected, other objects are not collected since weak references
          from Young Gen is handled as strong during CMC.

5. CMC_NO_SURV_ROOTS -  weakly referenced non-humongous and humongous objects are collected, softly referenced
                        non-humongous and humongous objects are not collected since we make 2 Young GC to promote all
                        weak references to Old Gen.

6. Mixed GC - weakly referenced non-humongous and humongous objects are collected, softly referenced non-humongous and
              humongous objects are not collected.

The test gets gc type as a command line argument.
Then the test allocates object graph in heap (currently testing scenarios are pre-generated and stored in
TestcaseData.getPregeneratedTestcases()) with TestObjectGraphAfterGC::allocateObjectGraph.

Since we are testing humongous objects we need pretty unusual nodes - arrays of Object.
We need this since only large enough array could be Humongous object (in fact class with huge amount of fields is
humongous too but it's for other tests).
ObjectGraph class generates object graph with Object[] nodes. It also provides a way to collect
information about each node using "visitor" pattern.

Using visitors we build Set of ReferenceInfo instances which contains the following information:
reference - external weak/soft reference to graph's node
graphId and nodeId - graph's and node's ids - we need this for error handling
softlyReachable - is node effectively referenced by external soft reference. It could be when external
soft reference or when this node is reachable from node that exteranally referenced by soft reference
effectiveHumongous - if node behaves effectively humongous.  It could be when node is humongous
or when this node is reachable from humongous node.

When we leave TestObjectGraphAfterGC::allocateObjectGraph we make graph reachable only with references from Set of
ReferenceInfo instances.

We run specified gc and check that each instance of ReferenceInfo set behaves as expected.
Then we check that gc log file contains expected tokens and doesn't contain tokens that it should not contain.