eiri commented on a change in pull request #1067: Fix mango native proc crash
URL: https://github.com/apache/couchdb/pull/1067#discussion_r157477887
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File path: src/mango/src/mango_native_proc.erl
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@@ -363,4 +366,35 @@ validate_index_info(IndexInfo) ->
[invalid_index | Results0]
end
end, [], IdxTypes),
- lists:member(valid_index, Results).
\ No newline at end of file
+ lists:member(valid_index, Results).
+
+
+-ifdef(TEST).
+
+-include_lib("eunit/include/eunit.hrl").
+
+handle_garbage_collect_cast_test() ->
+ Pid = self(),
+ {_, TracerRef} = spawn_monitor(fun() ->
+ erlang:trace(Pid, true, [garbage_collection]),
+ receive {trace, Pid, gc_start, _} ->
+ erlang:trace(Pid, false, [garbage_collection]),
+ exit(gc_start)
+ end
+ end),
+ erlang:yield(),
+ ?assertEqual({noreply, []}, handle_cast(garbage_collect, [])),
+ receive
+ {'DOWN', TracerRef, _, _, Msg} -> ?assertEqual(gc_start, Msg)
Review comment:
No, no, it's different.
We spawn and monitor a new process that sets a trace on the test process,
because process can't trace itself. Then in the test process we call a garbage
collection by executing `handle_cast(garbage_collect, [])` and asserting that
we are getting proper `noreply` response. The tracer receives `gc_start` trace
message, indicating that its target (the test process) started a garbage
collection and exits with reason `gc_start`. Because we are monitoring it in
our test process, we are receiving its exit reason and can assert that it was
indeed for a garbage collection.
Interesting bit here is `erlang:yield()` - we need to give a scheduler a
chance to run the tracer process or gc will be finished before the trace set.
Conceptually it's is not different from when we are mocking module with
`meck` and then waiting for some of its functions to be called, but I had to
use trace here because you can't mock `garbage_collection`. Plus, unlike mock,
this is a real deal, we are checking actual, not simulated functionality.
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