Although VectorClockConfigServerTest inherits from ConfigServerTestFixture, its tests assume that nothing else is ticking the ClusterTime. However, ConfigServerTestFixture installs an actual DistLockManager, which spawns a ReplSetDistLockPinger thread that performs writes, thereby ticking ClusterTime. If the timing is such that these writes happen before/during the VectorClockConfigServerTest tests, they can cause the tests to fail. Therefore VectorClockConfigServerTest should install a mock DistLockManager.