Blog Post: Some Elixir Testing Tricks

I’ll look into improving them in an Elixir PR this weekend!

Indeed. But since tags are handled by the compiler (they’re just attributes, you can register your own for anything via Module.register_attribute/3. This is how some tools like Absinthe register their documentation and such.

Interestingly, ExUnit also provides a register_attribute/2, which can be used to register attributes for use only in tests. They show up under context.registered, i.e.:

@fixture :foo
# registers as
context.registered.fixture == :foo

There’s also a sibling one for describe attributes, register_describe_attribute/2 and one for modules, register_module_attribute/2, which can be used as described.

I’ve used the TAP formatter in the past to check test names. You can also follow the red-green-red pattern of testing, where you make the tests deliberately fail on the first run, to check the setup. If the test is empty you’ll get a warning about it not being implemented, and if you just want to force a fail you can assert false.

Very well written and useful. Thx for sharing!

It prompted me to review the documentation of the ExUnit.Case module. I’ve never used tags before, but the examples you provide in the blogpost are very clear. I’d even argue that you could easily improve the existing docs on tags with an example from your post. I wouldn’t have guessed that the tags are passed into the setup callbacks, and take advantage of them (combined with the pattern matching superpowers) like you showed. Super handy indeed. It could as well have worked the other way: setup callbacks are run first, and the tag value is merged into the context last. That’s not clear from the current documentation on tags, afaik.

While reading up on the tag docs I also noticed that you can do:

@tag :admin

which is equivalent to:

@tag admin: true

This spares another four characters

The last part on how to generate tests with the for-comprehension prompted another question: can you run the tests in a way that it prints out all the test names that are run, also if they pass? When you’re generating tests like that, it’s nice to see the generated test name at least once, to see if it will make sens if they fail. I know you should start with a failing test, but still… Would be nice to have a formatter that prints more than just a green dot for every passing test. There is a CLI option to override the default formatter, but I didn’t find any bundled formatter that I could pass in.

I very much echo the “great article” sentiments and thank you for making me aware of TAP!

I have a somewhat similar helper as your assert_html for LiveView tests to narrow down text within a certain element which I find myself doing a fair bit often:

defmacro assert_within(lv, selector, text_or_regex) do
  quote do
    assert unquote(lv)
           |> element(unquote(selector))
           |> render() =~ unquote(text_or_regex)
  end
end

assert_within(lv, ".comments", "Product was definitely broken when it arrived, please send another.")