Deflake faster joins device list tests by waiting for leave event

[squahtx]

Many of the faster joins test flakes are due to the homeserver under
test failing to contact Complement homeservers after they have been
torn down. When this happens, subsequent tests can fail if they use a
Complement homeserver that happens to have the same hostname:port as one
which the homeserver under test has previously marked as offline.

Wait for the homeserver under test to finish broadcasting its leave at
the end of the device list tests.

Signed-off-by: Sean Quah seanq@matrix.org

---

Builds on top of #626.
Reviewable commit by commit.

NB: you can tease out the flakes by forcing Complement to reuse ports whenever possible:

diff --git a/internal/federation/server.go b/internal/federation/server.go
index ed7974d..4c4ccbe 100644
--- a/internal/federation/server.go
+++ b/internal/federation/server.go
@@ -455,7 +455,10 @@ func (s *Server) Listen() (cancel func()) {
        var wg sync.WaitGroup
        wg.Add(1)

-       ln, err := net.Listen("tcp", ":0") //nolint
+       ln, err := net.Listen("tcp", ":63333") //nolint
+       if err != nil {
+               ln, err = net.Listen("tcp", ":63334") //nolint
+       }
        if err != nil {
                s.t.Fatalf("ListenFederationServer: net.Listen failed: %s", err)
        }

[squahtx]

CI flaked due to the issue fixed by #628.

[DMRobertson]

Looks like this was painful to diagnose; thank you for persisting.

[DMRobertson]

I guess this is go's idiom for an optional argument? Feels a bit odd to allow an arbitrary length array/slice, but I guess it's easier than updating every call site?

[squahtx]

Not sure actually. Functional varargs (https://stackoverflow.com/a/26326418) is the pattern MustDoFunc uses. Here I didn't bother with them since there's only one optional argument.

[DMRobertson]

(I've optimistically marked this as closing a bunch of faster join device list updates tests---hope I correctly matched up tests to this issue)