Hi everyone,
With the upgrade of supported Erlang version and introduction of Elixir into
our integration test suite we have an opportunity to replace currently used
eunit (for new tests only) with Elixir based ExUnit.
The eunit testing framework is very hard to maintain. In particular, it has the
following problems:
- the process structure is designed in such a way that failure in setup or
teardown of one test affects the execution environment of subsequent tests.
Which makes it really hard to locate the place where the problem is coming from.
- inline test in the same module as the functions it tests might be skipped
- incorrect usage of ?assert vs ?_assert is not detectable since it makes tests
pass
- there is a weird (and hard to debug) interaction when used in combination
with meck
- https://github.com/eproxus/meck/issues/133#issuecomment-113189678
- https://github.com/eproxus/meck/issues/61
- meck:unload() must be used instead of meck:unload(Module)
- teardown is not always run, which affects all subsequent tests
- grouping of tests is tricky
- it is hard to group tests so individual tests have meaningful descriptions
We believe that with ExUnit we wouldn't have these problems:
- on_exit function is reliable in ExUnit
- it is easy to group tests using `describe` directive
- code-generation is trivial, which makes it is possible to generate tests from
formal spec (if/when we have one)
Here are a few examples:
# Test adapters to test different interfaces using same test suite
CouchDB has four different interfaces which we need to test. These are:
- chttpd
- couch_httpd
- fabric
- couch_db
There is a bunch of operations which are very similar. The only differences
between them are:
- setup/teardown needs different set of applications
- we need to use different modules to test the operations
This problem is solved by using testing adapter. We would define a common
protocol, which we would use for testing.
Then we implement this protocol for every interface we want to use.
```
defmodule Couch.Test.CRUD do
use ExUnit.Case
alias Couch.Test.Adapter
alias Couch.Test.Utils, as: Utils
alias Couch.Test.Setup
require Record
test_groups = [
"using Clustered API": Adapter.Clustered,
"using Backdoor API": Adapter.Backdoor,
"using Fabric API": Adapter.Fabric,
]
for {describe, adapter} <- test_groups do
describe "Database CRUD #{describe}" do
@describetag setup: %Setup{}
|> Setup.Start.new([:chttpd])
|> Setup.Adapter.new(adapter)
|> Setup.Admin.new(user: "adm", password: "pass")
|> Setup.Login.new(user: "adm", password: "pass")
test "Create", %{setup: setup} do
db_name = Utils.random_name("db")
setup_ctx = setup |> Setup.run()
assert {:ok, resp} = Adapter.create_db(Setup.get(setup_ctx, :adapter),
db_name)
assert resp.body["ok"]
end
end
end
end
```
# Using same test suite to compare new implementation of the same interface
with the old one
Imagine that we are doing a major rewrite of a module which would implement the
same interface.
How do we compare both implementations return the same results for the same
input?
It is easy in Elixir, here is a sketch:
```
defmodule Couch.Test.Fabric.Rewrite do
use ExUnit.Case
alias Couch.Test.Utils, as: Utils
# we cannot use defrecord here because we need to construct
# record at compile time
admin_ctx = {:user_ctx, Utils.erlang_record(
:user_ctx, "couch/include/couch_db.hrl", roles: ["_admin"])}
test_cases = [
{"create database": {create_db, [:db_name, []]}},
{"create database as admin": {create_db, [:db_name, [admin_ctx]]}}
]
module_a = :fabric
module_b = :fabric3
describe "Test compatibility of '#{module_a}' with '#{module_b}'" do
for {description, {function, args}} <- test_cases do
test "#{description}" do
result_a = unquote(module_a).unquote(function)(unquote_splicing(args))
result_b = unquote(module_b).unquote(function)(unquote_splicing(args))
assert result_a == result_b
end
end
end
end
```
As a result we would get following tests
```
Couch.Test.Fabric.Rewrite
* test Test compatibility of 'fabric' with 'fabric3' create database (0.01ms)
* test Test compatibility of 'fabric' with 'fabric3' create database as admin
(0.01ms)
```
The prototype of integration is in this draft PR
https://github.com/apache/couchdb/pull/2036. I am planing to write formal RFC
after first round of discussions on ML.
Best regards,
iilyak
