That's very helpful, thank you Myron.

We already keep several manifests for compiled code with the function
calls, files and modules. Therefore it should be relatively
straight-forward to keep one for tests. I think the first step is to build
the manifest itself which will give us the last_run_status information. Is
that right?

Implementation-wise, we can probably even use a custom "formatter" to
maintain this information. All we need is a path to store this manifest
(which is opt-in but mix test can generate one by default in _build and
pass to ExUnit).




*José Valimwww.plataformatec.com.br
<http://www.plataformatec.com.br/>Founder and Director of R&D*

On Thu, Nov 23, 2017 at 4:27 PM, Allen Madsen <[email protected]>
wrote:

> +1 for --next-failure functionality. My current approach with ExUnit is
> basically a manual version of that.
>
> Allen Madsen
> http://www.allenmadsen.com
>
> On Thu, Nov 23, 2017 at 12:28 PM, Myron Marston <[email protected]>
> wrote:
>
>> I believe this would be a good addition. My only question is where are
>> the failed tests stored? In _build?
>>
>> For RSpec we made users configure where this state is stored, via a
>> config.example_status_persistence_file_path option. RSpec didn’t have an
>> established place to write that state so we left it up to the user to
>> decide where they wanted it to go. I think for ExUnit, storing it in
>> _build make sense.
>>
>> However, note that we are not merely storing a list of failed tests. We
>> store a list of *all* tests (including ones that were not included in
>> the latest run) that looks like this:
>>
>> example_id                                                             | 
>> status  | run_time        |
>> ---------------------------------------------------------------------- | 
>> ------- | --------------- |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:1:1]                   | 
>> passed  | 0.00115 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:1:2]                   | 
>> passed  | 0.00052 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:1:3]                   | 
>> unknown |                 |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:1:4]                   | 
>> passed  | 0.00048 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:2:1:1]                 | 
>> passed  | 0.00058 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:2:2:1]                 | 
>> failed  | 0.00088 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:2:3:1]                 | 
>> passed  | 0.00084 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:3:1]                   | 
>> passed  | 0.00052 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:3:2]                   | 
>> failed  | 0.00059 seconds |
>> ./spec/rspec/core/backtrace_formatter_spec.rb[1:4:1]                   | 
>> pending | 0.00053 seconds |
>> ./spec/rspec/core/bisect/coordinator_spec.rb[1:1]                      | 
>> passed  | 0.00366 seconds |
>> ./spec/rspec/core/bisect/coordinator_spec.rb[1:2]                      | 
>> passed  | 0.00307 seconds |
>> ./spec/rspec/core/bisect/coordinator_spec.rb[1:3:1]                    | 
>> passed  | 0.002 seconds   |
>> ./spec/rspec/core/bisect/coordinator_spec.rb[1:3:2]                    | 
>> passed  | 0.00231 seconds |
>> ./spec/rspec/core/bisect/coordinator_spec.rb[1:4:1]                    | 
>> passed  | 0.00293 seconds |
>> ./spec/rspec/core/bisect/example_minimizer_spec.rb[1:1]                | 
>> passed  | 0.00049 seconds |
>> ./spec/rspec/core/bisect/example_minimizer_spec.rb[1:2]                | 
>> passed  | 0.0006 seconds  |
>>
>> # ...
>>
>> This is a custom serialization format we designed to be easily scannable
>> by a human (as it’s useful information, particular the run_time). The
>> example_id column uniquely identifies each test (since the other common
>> ways to identify tests, such as description and file location, are not
>> guaranteed to be unique). Every time a test run finishes, we merge the
>> results with the existing contents of this file using a few simple rules
>> <https://github.com/rspec/rspec-core/blob/v3.7.0/lib/rspec/core/example_status_persister.rb#L66-L72>
>> .
>>
>> We then use this data to automatically add :last_run_status metadata to
>> every test (with values of passed, failed, pending or unknown) when the
>> spec files are loaded, which unlocks the generic ability to filter based on
>> this via the RSpec CLI:
>>
>> $ rspec --tag last_run_status:failed
>>
>> This is the equivalent of --only failed like you asked about, José.
>> Whether or not you add an explicit option like --only-failures is up to
>> you, but the explicit option does provide a couple nice advantages for
>> RSpec:
>>
>>    - It surfaces this extremely useful option in the --help output.
>>    Without calling it out, it would not be clear to most users that failure
>>    filtering is possible.
>>    - Since we can easily tell from our persistence file which spec files
>>    have failures, when --only-failures is passed, we automatically load
>>    only those files. In contrast, --tag filtering doesn’t generally know
>>    anything in advance about which files might have specs matching the tag, 
>> so --tag
>>    last_run_status:failed will load *all* spec files, and then apply the
>>    filtering. This can be significantly slower, particularly if there are
>>    files without failures that load a heavyweight dependency (like rails).
>>
>> One other option we provide (which ExUnit may or may not want to provide)
>> is --next-failure. This is the equivalent of --only-failures --fail-fast
>> --order defined. The idea is that you often want to work through the
>> failures systematically one-by-one. --fail-fast causes RSpec to abort as
>> soon as the first failure is hit and --order defined disables the random
>> ordering so you get the same failed example when you run rspec
>> --next-failure over and over again to help you focus on a specific one.
>> This option is also why we do the merging operation with the status from
>> prior runs: it’s important that we preserve the failed status of tests
>> that weren’t executed in the latest run.
>>
>> ExUnit certainly doesn’t have to go the same route RSpec went here, but
>> the combination of the perf speed up from avoiding loading files with only
>> passing tests and the usefulness of --next-failure is pretty awesome,
>> IMO.
>> ​
>> Myron
>>
>>
>> On Thu, Nov 23, 2017 at 4:03 AM, José Valim <[email protected]> wrote:
>>
>>> Thanks everyone!
>>>
>>> I believe this would be a good addition. My only question is where are
>>> the failed tests stored? In _build? Also, maybe we can also implement it as
>>> a special tag called "--only failed" or "--only failures"?
>>>
>>>
>>>
>>>
>>> *José Valimwww.plataformatec.com.br
>>> <http://www.plataformatec.com.br/>Founder and Director of R&D*
>>>
>>> On Thu, Nov 23, 2017 at 6:03 AM, Myron Marston <[email protected]>
>>> wrote:
>>>
>>>> I too would love to see ExUnit support an `--only-failures` flag.  It's
>>>> one of my favorite features of RSpec and I wish every test framework had
>>>> it.  I find that it makes a huge difference to my workflow to be able to
>>>> quickly and easily filter to the tests that failed the last time they ran.
>>>>
>>>> In fact, I love this feature of RSpec so much that I was the one who
>>>> added it to the framework a couple years back :).  I'd be happy to help see
>>>> it get added to ExUnit if José and others were amenable.  ExUnit already
>>>> has most of the building blocks needed for it via tags and filtering.
>>>>
>>>> Myron
>>>>
>>>> On Wednesday, November 22, 2017 at 2:48:14 PM UTC-8, José Valim wrote:
>>>>>
>>>>> To clarify, --stale does not run previously failed tests.
>>>>>
>>>>> > I just changed the format of the message built within
>>>>> `MyApp.Mixpanel`. This caused `assert_receive` to fail in tests throughout
>>>>> my app, as expected. But since the tests didn't directly reference
>>>>> `MyApp.Mixpanel`, `--stale` didn't know which ones should be run when the
>>>>> message format changed; I had to run all tests to get them to fail.
>>>>>
>>>>> That feels like a bug. Maybe we are being conservative on how we
>>>>> compute the dependencies. If you can provide a sample app that reproduces
>>>>> the error, I would love to take a look at it.
>>>>>
>>>>>
>>>>>
>>>>> *José Valimwww.plataformatec.com.br
>>>>> <http://www.plataformatec.com.br/>Founder and Director of R&D*
>>>>>
>>>>> On Wed, Nov 22, 2017 at 8:06 PM, Nathan Long <[email protected]>
>>>>> wrote:
>>>>>
>>>>>> Sure. I have a module called `MyApp.Mixpanel` with functions like
>>>>>> `track_event(:user_signup, data_map)`. These are called from various 
>>>>>> places
>>>>>> throughout the codebase. There's a production adapter, which actually 
>>>>>> sends
>>>>>> the event data to Mixpanel for analytics purposes, a dev adapter, which
>>>>>> just logs it, and a test adapter, which sends it to `self()` as a 
>>>>>> message.
>>>>>>
>>>>>> Several of my tests say things like "if I POST the info required for
>>>>>> a new user signup, I should get a message showing that the correct info
>>>>>> would have been sent to Mixpanel." These use `assert_receive`.
>>>>>>
>>>>>> I just changed the format of the message built within
>>>>>> `MyApp.Mixpanel`. This caused `assert_receive` to fail in tests 
>>>>>> throughout
>>>>>> my app, as expected. But since the tests didn't directly reference
>>>>>> `MyApp.Mixpanel`, `--stale` didn't know which ones should be run when the
>>>>>> message format changed; I had to run all tests to get them to fail.
>>>>>>
>>>>>> This is no big deal, but it would be nice in such situations to run
>>>>>> all tests once, then be able to whittle down the failing tests without
>>>>>> re-running the whole suite.
>>>>>>
>>>>>> On Wednesday, November 22, 2017 at 4:54:51 PM UTC-5, Louis Pilfold
>>>>>> wrote:
>>>>>>>
>>>>>>> Hi Nathan
>>>>>>>
>>>>>>> I feel ExUnit --stale should always be able to tell this. Could you
>>>>>>> share your example please?
>>>>>>>
>>>>>>> Cheers,
>>>>>>> Louis
>>>>>>>
>>>>>>> On Wed, 22 Nov 2017 at 20:43 Nathan Long <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Ruby's Rspec has a handy option, `--only-failures`, which "filters
>>>>>>>> what examples are run so that only those that failed the last time 
>>>>>>>> they ran
>>>>>>>> are executed". https://relishapp.com/rspec/rs
>>>>>>>> pec-core/docs/command-line/only-failures
>>>>>>>>
>>>>>>>> I'd love to have this feature in ExUnit. The closest thing I see
>>>>>>>> right now is `--stale`, but if ExUnit can't accurately determine which
>>>>>>>> tests may have been broken by a change, it doesn't work. (I have such 
>>>>>>>> an
>>>>>>>> example, but don't want to be long-winded; maybe the utility of this
>>>>>>>> feature is clear enough?)
>>>>>>>>
>>>>>>>> --
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