#7836 serverset::tests::backoff_when_unhealthy is flaky Issue created by stuhood Seen in https://travis-ci.org/pantsbuild/pants/jobs/540442640: ``` test tests::backoff_when_unhealthy ... thread 'tokio-runtime-worker-1' panicked at 'assertion failed:

(left == right)

left:

"good"

, right: `"bad"`', serverset/src/lib.rs47913 stack backtrace: 0: std:sysunixbacktracetracing👿:unwind_backtrace at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39 1: std:sys commonbacktrace:_print at src/libstd/sys_common/backtrace.rs:71 2: std:panickingdefault hook:{{closure}} at src/libstd/sys_common/backtrace.rs:59 at src/libstd/panicking.rs:197 3: std:panicking:default_hook at src/libstd/panicking.rs:211 4: <std:panickingbegin panic:PanicPayload<A> as core:panicBoxMeUp&gt;:get at src/libstd/panicking.rs:474 5: std:panicking:continue_panic_fmt at src/libstd/panicking.rs:381 6: std:panickingtry:do_call at src/libstd/panicking.rs:336 7: serverset:testsexpect only good:{{closure}} at serverset/src/lib.rs:479 8: core:resultResult&lt;T,E&gt;:map at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libcore/result.rs:458 9: <futures:futuremap:Map<A,F> as futures:futureFuture&gt;:poll at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/future/map.rs:35 10: futures:futurechainChain&lt;A,B,C&gt;:poll at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/future/chain.rs:26 11: <futures:futurethen:Then<A,B,F> as futures:futureFuture&gt;:poll at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/future/then.rs:32 12: <futures:task impl:NotifyHandle as core:cloneClone&gt;:clone at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/future/mod.rs:113 13: futures:task implNotifyHandle:new at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/mod.rs:329 14: futures:task implNotifyHandle:new at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/mod.rs:399 15: futures:task implstdCURRENT THREAD NOTIFY:__init at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/std/mod.rs:83 16: futures:task implNotifyHandle:new at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/mod.rs:399 17: futures:task implNotifyHandle:new at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/mod.rs:291 18: futures:task implNotifyHandle:new at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.27/src/task_impl/mod.rs:329 19: tokio_threadpool:taskTaskrun:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/task/mod.rs:145 20: core:opsfunctionFnOnce:call_once at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libcore/ops/function.rs:231 21: tokio_threadpool:parkdefault parkDefaultPark:park_sync at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/panic.rs:309 22: crossbeam_utils:backoffBackoff:snooze at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/panicking.rs:293 23: panic_unwind:dwarfeh:read_encoded_pointer at src/libpanic_unwind/lib.rs:87 24: crossbeam_utils:backoffBackoff:snooze at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/panicking.rs:272 25: crossbeam_utils:backoffBackoff:snooze at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/panic.rs:388 26: tokio_threadpool:taskTask:run at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/task/mod.rs:130 27: tokio_threadpool:workerWorker:run_task2 at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/worker/mod.rs:567 28: tokio_threadpool:workerWorker:run_task at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/worker/mod.rs:459 29: tokio_threadpool:workerWorker:try_run_owned_task at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/worker/mod.rs:390 30: tokio_threadpool:workerWorker:try_run_task at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/worker/mod.rs:297 31: tokio_threadpool:workerWorkerwith current:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-threadpool-0.1.12/src/worker/mod.rs:241 32: tokio:runtimethreadpoolbuilderBuilderbuild{{closure}}{{closure}}{{closure}}{{closure}}:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.1.17/src/runtime/threadpool/builder.rs:349 33: futures:task implstdCURRENT THREAD NOTIFY:__init at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-trace-core-0.1.0/src/dispatcher.rs:54 34: tokio:runtimethreadpoolbuilderBuilderbuild{{closure}}{{closure}}{{closure}}:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.1.17/src/runtime/threadpool/builder.rs:348 35: <tokio_reactor::HandlePriv as core:cloneClone&gt;:clone at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-timer-0.2.10/src/timer/handle.rs:94 36: alloc:raw vec:alloc_guard at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/thread/local.rs:299 37: alloc:raw vec:alloc_guard at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/thread/local.rs:245 38: <tokio_reactor::HandlePriv as core:cloneClone&gt;:clone at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-timer-0.2.10/src/timer/handle.rs:81 39: tokio:runtimethreadpoolbuilderBuilderbuild{{closure}}{{closure}}:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.1.17/src/runtime/threadpool/builder.rs:347 40: futures:task implcore:get_ptr at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-timer-0.2.10/src/clock/clock.rs:141 41: alloc:raw vec:alloc_guard at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/thread/local.rs:299 42: alloc:raw vec:alloc_guard at /rustc/3c235d5600393dfe6c36eeed34042efad8d4f26e/src/libstd/thread/local.rs:245 43: futures:task implcore:get_ptr at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-timer-0.2.10/src/clock/clock.rs:124 44: tokio:runtimethreadpoolbuilderBuilderbuild{{closure}}:{{closure}} at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec823/tokio-0.1.17/src/runtime/threadpool/builder.rs:346 45: alloc:raw vec:alloc_guard at /Users/travis/.cache/pants/rust/cargo/registry/src/github.com-1ecc6299db9ec82… pantsbuild/pants