Unit test for NetworkTopologyStrategy class.
Creates a dummy cluster topology: token ring, token_metadata, snitch (RackInferringSnitch).
Then requests a natural endpoints for tokens that lay between each two adjacent ring tokens
and verifies the output.
It also checks the natural_endpoints caching:
1) Verifies that the result is calculated when we query the specific token_ring point
for the first time.
2) Verifies that the result is taken from the cache when we query the specific token_ring
point for the second time.
3) Verifies that the results in (1) and (2) are identical.
4) Verifies that the cache is invalidated after token_metadata::invalidate_cached_rings()
is called.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
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