<p>Non-negative integer less than or equal to 50;
optional</p>

<p>Specifies the number of parallel shards
to use to run the test.</p>

<p>This value will override any heuristics used to determine the number of
parallel shards with which to run the test. Note that for some test
rules, this parameter may be required to enable sharding
in the first place. Also see <code>--test_sharding_strategy</code>.</p>

<p>Sharding requires the test runner to support the test sharding protocol.
If it does not, then it will most likely run every test in every shard, which
is not what you want.</p>