Add unit tests for GenServer callbacks in ThousandIsland.Listener

[thymusvulgaris]

Adds unit tests for the following GenServer callbacks in ThousandIsland.Listener:

• init/1
• handle_call/3
• terminate/2

[thymusvulgaris]

The following CI failure:

 1) test shutdown it should emit telemetry events as expected (ThousandIsland.ServerTest)
Error:      test/thousand_island/server_test.exs:309
     Assertion with ~> failed
     
     Mismatches:
     
       1) List is 3 elements in length, expected 4
     
     code: assert ThousandIsland.TelemetryCollector.get_events(collector_pid)
           ~> [
             {[:thousand_island, :listener, :start], %{monotonic_time: integer()},
              %{
                telemetry_span_context: reference(),
                local_address: {0, 0, 0, 0},
                local_port: integer(),
                transport_module: ThousandIsland.Transports.TCP,
                transport_options: []
              }},
             {[:thousand_island, :acceptor, :start], %{monotonic_time: integer()},
              %{telemetry_span_context: reference(), parent_telemetry_span_context: reference()}},
             {[:thousand_island, :listener, :stop], %{duration: integer(), monotonic_time: integer()},
              %{
                telemetry_span_context: reference(),
                local_address: {0, 0, 0, 0},
                local_port: integer(),
                transport_module: ThousandIsland.Transports.TCP,
                transport_options: []
              }},
             {[:thousand_island, :acceptor, :stop],
              %{connections: 0, duration: integer(), monotonic_time: integer()},
              %{telemetry_span_context: reference(), parent_telemetry_span_context: reference()}}
           ]
     stacktrace:
       test/thousand_island/server_test.exs:325: (test)

..............
Finished in 11.3 seconds (0.00s async, 11.3s sync)
54 tests, 1 failure

was replicated locally by running:

$ for i in {1..10}; do mix test test/thousand_island/server_test.exs >> acceptor.test.log; done

$ cat acceptor.test.log
.............
Finished in 5.5 seconds (0.00s async, 5.5s sync)
13 tests, 0 failures

Randomized with seed 68044
.............
Finished in 5.5 seconds (0.00s async, 5.5s sync)
13 tests, 0 failures

Randomized with seed 835196
.............
Finished in 5.4 seconds (0.00s async, 5.4s sync)
13 tests, 0 failures

Randomized with seed 542935


  1) test shutdown it should emit telemetry events as expected (ThousandIsland.ServerTest)
     test/thousand_island/server_test.exs:309
     Assertion with ~> failed
     
     Mismatches:
     
       1) List is 3 elements in length, expected 4
     
     code: assert ThousandIsland.TelemetryCollector.get_events(collector_pid)
           ~> [
             {[:thousand_island, :listener, :start], %{monotonic_time: integer()},
              %{
                telemetry_span_context: reference(),
                local_address: {0, 0, 0, 0},
                local_port: integer(),
                transport_module: ThousandIsland.Transports.TCP,
                transport_options: []
              }},
             {[:thousand_island, :acceptor, :start], %{monotonic_time: integer()},
              %{telemetry_span_context: reference(), parent_telemetry_span_context: reference()}},
             {[:thousand_island, :listener, :stop], %{duration: integer(), monotonic_time: integer()},
              %{
                telemetry_span_context: reference(),
                local_address: {0, 0, 0, 0},
                local_port: integer(),
                transport_module: ThousandIsland.Transports.TCP,
                transport_options: []
              }},
             {[:thousand_island, :acceptor, :stop],
              %{connections: 0, duration: integer(), monotonic_time: integer()},
              %{telemetry_span_context: reference(), parent_telemetry_span_context: reference()}}
           ]
     stacktrace:
       test/thousand_island/server_test.exs:325: (test)

............
Finished in 5.4 seconds (0.00s async, 5.4s sync)
13 tests, 1 failure

Randomized with seed 195071
.............
Finished in 5.5 seconds (0.00s async, 5.5s sync)
13 tests, 0 failures

Randomized with seed 851493
.............
Finished in 5.4 seconds (0.00s async, 5.4s sync)
13 tests, 0 failures

Randomized with seed 614251
.............
Finished in 5.5 seconds (0.00s async, 5.5s sync)
13 tests, 0 failures

Randomized with seed 268188
.............
Finished in 5.5 seconds (0.00s async, 5.5s sync)
13 tests, 0 failures

Randomized with seed 46400
.............
Finished in 6.0 seconds (0.00s async, 6.0s sync)
13 tests, 0 failures

Randomized with seed 838041
.............
Finished in 5.4 seconds (0.00s async, 5.4s sync)
13 tests, 0 failures

Randomized with seed 197235

[mtrudel]

Yeah, the telemetry tests in particular are known to be a bit racy.

Looks great!