Many of our tests rely on helpers that predate features which are now
available in the standard library.
This patch replaces them with the standard equivalents:
- MustTempDir/RemoveIfOk -> t.ArtifactDir() or t.TempDir() (depending on
whether it is useful to keep the data on request).
- GetFreePort + waitForServer -> opening the listeners before starting
the servers. To support this, localrpc.Server gains a Serve method. We
may re-introduce these in the future if more use cases appear.
- WaitFor and real-time timing checks -> testing/synctest.
- context.Background() -> t.Context().
- Benchmark b.N loops -> b.Loop().
- reflect.DeepEqual -> cmp.Diff, and proto.Equal for protobufs.
staticcheck found a couple of minor code cleanup improvements, like
unused variables or an out-of-order defer, mostly in tests.
This patch fixes those problems by making the necessary adjustments.
They're all fairly small, and should not change the logic in any
significant way.