Cranking Up Code Coverage #
$ mix test --cover
Several different kinds of tests:
- Logic unit tests, mostly for pure code.
- Context unit tests, for simple DB actions and verifying schema/changeset logic.
- Controller tests / LiveView tests, to that some specific request/ response action by the user works as expected.
- Integration tests test sequences of actions, possibly entire standard workflows.
That’s before we even get to:
- Testing JS code.
- Popping up a full browser to test everything “for real”.
Let’s pick out a couple modules and manually write some tests, optimally of different kinds.
And then, AI tools are pretty good at writing tests, so let’s use Aider here. I think I’ve got my laptop set to use Cerebras for Quen3-Coder, so it should be able to generate code fast.
If we can, let’s get coverage up to 25% and then crank up the threshold in mix.exs
Credo - Static Analysis / Style Rules #
Start at: https://github.com/rrrene/credo
- Add to mix.exs
mix deps.getmix credo gen.configmix credo
Those checks are great, but the check I want is for maximum file length:
mix credo.gen.check lib/shard/credo/max_file_length.ex
# .credo.exs
{Shard.Credo.MaxFileLength, max_lines: 400},
And the module:
defmodule Shard.Credo.MaxFileLength do
@moduledoc """
Count lines, complain if it exceeds a value.
"""
# you can configure the basics of your check via the `use Credo.Check` call
use Credo.Check, base_priority: :high, category: :custom, exit_status: 0
@default_params max_lines: 400
@doc false
@impl true
def run(%SourceFile{} = source_file, params) do
max_lines = params |> Params.get(:max_lines, __MODULE__)
lines = SourceFile.lines(source_file)
count = length(lines)
if count > max_lines do
issue =
format_issue(
IssueMeta.for(source_file, params),
message: "File is too long: #{count} > max of #{max_lines}",
trigger: source_file.filename
)
[issue]
else
[]
end
end
end
Let’s get everything run in CI #
- name: Install dependencies
run: mix deps.get
- name: Verify that this builds
run: mix compile --warnings-as-errors
- name: Check formatting
run: mix format --check-formatted
- name: Run tests
run: mix test
- name: Check coverage
run: mix test --cover
- name: Static Analysis
run: mix credo
