| Overview |  |
Functions for testing execution of Telemetry events.
Testing that the correct Telemetry events are emitted with the right measurements and metadata is essential for library authors. It helps to maintain stable APIs and avoid accidental changes to events.| attach_event_handlers/2 | Attaches a "message" handler to the given events. |
attach_event_handlers(DestinationPID, Events) -> reference()
DestinationPID = pid()Events = [telemetry:event_name(), ...]
Attaches a "message" handler to the given events.
The attached handler sends a message to destination_pid every time it handles one of the
events in events. The function returns a reference that you can use to make sure that
messages come from this handler. This reference is also used as the handler ID, so you
can use it to detach the handler with telemetry:detach/1.
The shape of messages sent to destination_pid is:
{Event, Ref, Measurements, Metadata}
For example, in Erlang a test could look like this:
Ref = telemetry_test:attach_event_handlers(self(), [[some, event]]),
function_that_emits_the_event(),
receive
{[some, event], Ref, #{measurement := _}, #{meta := _}} ->
telemetry:detach(Ref)
after 1000 ->
ct:fail(timeout_receive_attach_event_handlers)
end.
In Elixir, a similar test would look like this:
ref = :telemetry_test.attach_event_handlers(self(), [[:some, :event]])
function_that_emits_the_event()
assert_received {[:some, :event], ^ref, %{measurement: _}, %{meta: _}}
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