How do I disable the error logger in EUnit test cases? - erlang

Question

When running an EUnit test that tests an application or starts and stops (or tests killing of) gen_server or supervisor processs, error logger outputs crash reports and other messages by default:
$ rebar3 eunit 1s
===> Verifying dependencies...
===> Compiling my_app
===> Performing EUnit tests...
...........=INFO REPORT==== 5-Sep-2019::16:32:18.760457 ===
application: ranch
exited: stopped
type: temporary
=INFO REPORT==== 5-Sep-2019::16:32:18.760545 ===
application: xmerl
exited: stopped
type: temporary
=INFO REPORT==== 5-Sep-2019::16:32:18.763882 ===
application: my_app
exited: stopped
type: temporary
......=ERROR REPORT==== 5-Sep-2019::16:32:18.814431 ===
** Generic server my_app_sup terminating
** Last message in was {'EXIT',<0.279.0>,test_kill}
** When Server state == {state,
{local,my_app_sup},
simple_one_for_one,
{[undefined],
#{undefined =>
{child,undefined,undefined,
{my_app_server,start_link,[]},
transient,5000,worker,
[my_app_server]}}},
{maps,#{<0.355.0> => [my_app_test]}},
1,5,[],0,my_app_sup,[]}
** Reason for termination ==
** test_kill
=CRASH REPORT==== 5-Sep-2019::16:32:18.814598 ===
crasher:
initial call: supervisor:my_app_sup/1
pid: <0.354.0>
registered_name: my_app_sup
exception exit: test_kill
in function gen_server:decode_msg/9 (gen_server.erl, line 432)
ancestors: [<0.279.0>]
message_queue_len: 0
messages: []
links: []
dictionary: []
trap_exit: true
status: running
heap_size: 1598
stack_size: 27
reductions: 6463
neighbours:
...........
Finished in 0.457 seconds
28 tests, 0 failures
How can I avoid these expected messages during testing?

Answer 1

These can be avoided by temporarily disabling TTY reports in the error logger. Surround the code which produces the reports with this:
my_test() ->
error_logger:tty(false),
try
% code that produces error logger reports
after
error_logger:tty(true)
end.
If you use this many times in the tests, this wrapper can be useful:
without_error_logger(Fun) ->
error_logger:tty(false),
try
Fun()
after
error_logger:tty(true)
end.
Which is used like so:
without_error_logger(fun() ->
% code that produces error logger reports
end)