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From Jan Lehnardt <>
Subject Re: [RFC] On the Testing of CouchDB
Date Sat, 16 Dec 2017 11:18:29 GMT

this is really cool. Im very happy to see progress on our test suites
and this looks like a great way forward.

A little bit more context on the JS suite and its runtime environment
couchjs: couchjs was never meant to be a general purpose JS execution
environment. We started using couchjs for the JS test suite because it
was already available in CouchDB and we were using JS tests as opposed
to Erlang tests because they were meant as initial documentation of
CouchDBs API. That was before the wiki was useful and dedicated docs
were nowhere in sight.

We are even maintaining a custom, C-based HTTP client so we can use
couchjs for HTTP tests. I’d be very happy to get rid of that code.

Today, there are better JS runtimes that are easy to use, and the JS
tests changed purpose from being documentation to being the source of
validation for a lot of API quirks in CouchDB that are not encoded
anywhere else outside of CouchDB. That’s why it is useful to keep the
knowledge inside the JS test suite around, but bring it forward to a
more usable execution environment.

* * *

When we’ve discussed the JS test suite in the past, we talked about
joining forces with the PouchDB team, since they have a version of our
JS tests running, with many good additions. Going with Elixir, we’re
closing the door on that particular collaboration, but given that this
has been discussed for 2+ years and not much happened, I’m okay with the
Elixir suite. The pouchdb-server project will be able to use the Elixir
suite just as we do.

The one thing that would be nice here if it were easy to disable certain
tests or suites that make no sense in the pouchdb-server environment, so
they can easily integrate it in their CI.

* * *

One of the problems with the JS tests is that they predate testing best
practices. The majority of tests are single functions with sometimes
hundreds of assertions and changes in configuration and mock data. This
is not very maintainable. The stats.js tests are split up more
traditionally, but that effort was never extended to the other test

I was happy to see that the Elixir port of the basics.js tests took a
sensible approach breaking things up in the way a modern test suite
would be done. Advantages include better isolation of specific behaviour
tests, ease of understanding tests, simpler running of individual tests
during development, more chances to structure and re-use mock data and
other boilerplate code, all making any work with the tests more pleasant.

It would be great if we could use this opportunity to apply this across
all JS test files when we port them to Elixir. It means a little bit
more work per test file, but I hope with a few more contributors and
guidelines, this is an easily paralleliseable task, so individual burden
can be minimised.

* * *

I noticed that one of the reduce tests took 30+ seconds to run on my
machine and I experimented with different cluster configuration values
and to nobodys surprise, the default of q=8 is the main factor in view
test execution speed. q=4 takes ~20s, q=2 ~10s and q=1 ~5s. I’m not
suggesting we set q=1 for all tests since q>1 is a behaviour we would
want to test as well, but maybe we can set q=2 when running the test
suite(s) for the time being. Shaving 25s off of a single test will get
us a long way with all tests ported. What do others think?

@Nick: you introduced the -C / --config-overrides option to dev/run,
but I could never figure out how to apply it. That would be the easiest
place to make the cluster config change for the Elixir tests.

`-c q=2` makes the nodes fail to start and I’m not sure how in this case,
the `[cluster]` section is meant.

* * *

Russell, Paul: do you think it is worth reaching out to the Elixir
community and ask if they are interested in helping out a little? If
you think its too early, we can wait with this.

* * *

Thanks again!


> On 15. Dec 2017, at 02:03, Russell Branca <> wrote:
> Howdy folks!
> The testing of CouchDB is something that has seen focus and improvements
> for the last several years, for instance migrating the etap suite to eunit,
> and updating the JS suite to run against clusters in 2.x. There's still
> improvements to be made, and that was one of the topics of the CouchDB dev
> summit early in the year [1].
> Before we go further, I want to clarify some nomenclature. I'm by no means
> going to try and define unit testing vs integration testing vs quantum
> phase shift testing, but instead I want to focus on the distinction of
> where the testing takes place. Fundamentally, we have two places we test
> CouchDB: 1) at the Erlang VM level where we conduct assertions against
> module functions or process states; 2) at the HTTP level where we test the
> behavior of CouchDB at the user level API. This post focuses entirely on
> the latter; that's not to say the former doesn't also merit attention, just
> that the two are different enough that we can focus on them in isolation.
> So with that, let's chat about the current HTTP test suite in CouchDB. This
> is the "JS suite" I referred to above, which is a custom built test suite
> written in Javascript and executed in the aging SpiderMonkey. The JS suite
> has put in work for years, but it's showing it's age, and is a bit awkward
> to work with and improve. However, I think the biggest issue with the JS
> suite is that it's utilized far less than it should be, and folks seem to
> avoid extending it or adding additional tests to it. There's been
> discussion for years about replacing said suite, but the discussions
> invariably got blocked on the bike shed of whether to rewrite the suite in
> Javascript or Python. This thread provides a third option, with code!
> I started hacking on a replacement for the JS suite, this time written in
> Elixir. Overall I'm quite impressed with how it's come along, and have some
> good examples to show. This is basically an Elixir app that has an HTTP
> client and then runs a series of tests that conduct tests against the
> CouchDB HTTP API and make assertions therein.
> You can find the current code in [2], and a comparison of the changes in
> [3]. The core HTTP client is only a handful of lines of codes and works
> quite well [4]. The utility functions used across all tests are located in
> [5], and the tests themselves are in [6]. The existing test modules have a
> 1:1 correspondence with the associated JS suite test modules, and in
> general are as direct of a port as possible.
> The test modules ported in their entirety or most of the way are:
>  * all_docs.js
>  * basics.js
>  * config.js
>  * reduce.js
>  * rewrite.js
>  * uuids.js
>  * view_collation.js
> Paul has dove in and is responsible for a few of those test modules and
> he's almost completed porting the replication.js suite as well. We started
> with the hard ones first, so for the most part the rest of the ports should
> be fairly smooth sailing.
> Here's an example of a very basic test:
> ```erlang
> defmodule WelcomeTest do
>  use CouchTestCase
>  test "Welcome endpoint" do
>    assert Couch.get("/").body["couchdb"] == "Welcome", "Should say welcome"
>  end
> end
> ```
> As you can see, the `Couch` client is very simple HTTP client with
> easy HTTP verb based methods. Let's look at a more complicated test
> for asserting we can create documents in a database:
> ```erlang
>  @tag :with_db
>  test "Create a document and save it to the database", context do
>    resp ="/#{context[:db_name]}", [body: %{:_id => "0",
> :a => 1, :b => 1}])
>    assert resp.status_code == 201, "Should be 201 created"
>    assert resp.body["id"], "Id should be present"
>    assert resp.body["rev"], "Rev should be present"
>    resp2 = Couch.get("/#{context[:db_name]}/#{resp.body["id"]}")
>    assert resp2.body["_id"] == resp.body["id"], "Ids should match"
>    assert resp2.body["_rev"] == resp.body["rev"], "Revs should match"
>  end
> ```
> This is fairly straightforward code to POST a new doc, make assertions
> on the response, and then fetch the doc to make sure everything
> matches up. What I really wanted to highlight here is the `@tag
> :with_db` decorator. We can easily add custom "tags" to the tests to
> simplify setup and teardown. That `:with_db` tag does two things, it
> dynamically generates a random database name, and then takes care of
> setup/teardown for creating and deleting said database for that
> particular test. This is really useful and has been very nice to work
> with so far. We also have tag functionality in place for executing a
> test with a particular set of config options:
> ```erlang
>  @tag config: [
>    {"uuids", "algorithm", "utc_random"}
>  ]
>  test "utc_random uuids are roughly random" do
>    resp = Couch.get("/_uuids", query: %{:count => 1000})
>    assert resp.status_code == 200
>    uuids = resp.body["uuids"]
>    assert String.length(, 1)) == 32
>    # Assert no collisions
>    assert length(Enum.uniq(uuids)) == length(uuids)
>    # Assert rough ordering of UUIDs
>    u1 = String.slice(, 1), 0..13)
>    u2 = String.slice(, -1), 0..13)
>    assert u1 < u2
>  end
> ```
> The tag system really simplifies a lot of the standard auxiliary
> actions needed to conduct tests.
> To test out the suite, you'll need to spin up the dev server in one window with:
> ```
> ./dev/run --admin=adm:pass
> ```
> and then in another window go into the relevant CouchDB src directory and run:
> ```
> cd ~/src/couchdb/elixir_suite/
> mix deps.get
> mix test --trace
> ```
> The `--trace` flag makes the nice line item output per test, which I
> greatly prefer over a slew of periods. You can run an individual test
> with `mix test --trace tests/basics_test.exs`. I've pasted the output
> from running the basics suite at the bottom of this email so you can
> see what the real output looks like.
> Overall I'm quite impressed with the toolkit we've been able to put
> together in a short amount of time, and I propose we migrate fully to
> this test suite by porting all remaining JS suite tests and then
> removing the JS suite entirely. Given we've already ported most of the
> "hard suites", I think a full port is reasonable to do and just
> requires some leg work. Again, I'm impressed with how simple the
> tooling here is and how quickly we've been able to run with things,
> turns out the Elixir dev experience is actually quite nice! I hope
> others have similar opinions after diving in! Let me know what you
> think.
> -Russell
> [1]
> [2]
> [3]
> [4]
> [5]
> [6]
> vagrant@contrib-jessie:~/src/couchdb/elixir_suite$ mix test --trace
> test/basics_test.exs
> Excluding tags: [pending: true]
> BasicsTest
>  * test Session contains adm context (66.8ms)
>  * test Creating a new DB with slashes should return Location header
> (COUCHDB-411) (85.8ms)
>  * test oops, the doc id got lost in code nirwana (82.1ms)
>  * test Welcome endpoint (7.6ms)
>  * test POST doc with an _id field isn't overwritten by uuid (102.7ms)
>  * test On restart, a request for creating an already existing db can
> not override (skipped)
>  * test Creating a new DB should return location header (118.7ms)
>  * test _bulk_docs POST error when body not an object (95.0ms)
>  * test Empty database should have zero docs (161.0ms)
>  * test _all_docs POST error when multi-get is not a {'key': [...]}
> structure (104.3ms)
>  * test Regression test for COUCHDB-954 (skipped)
>  * test DELETE'ing a non-existent doc should 404 (100.0ms)
>  * test Revs info status is good (127.3ms)
>  * test PUT on existing DB should return 412 instead of 500 (97.6ms)
>  * test Database should be in _all_dbs (117.7ms)
>  * test Check for invalid document members (122.4ms)
>  * test Can create several documents (213.0ms)
>  * test Make sure you can do a seq=true option (99.1ms)
>  * test PUT doc has a Location header (skipped)
>  * test Create a document and save it to the database (116.3ms)
>  * test Created database has appropriate db info name (99.7ms)
>  * test PUT error when body not an object (89.5ms)
>  * test Simple map functions (473.0ms)
>  * test POST doc response has a Location header (117.1ms)
> CouchTestCase
> Finished in 3.3 seconds
> 24 tests, 0 failures, 3 skipped
> Randomized with seed 936284

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