Custom Assertions

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Custom Assertions

Create a CustomAssertion.assert macro which provides test feedback in the format:

"""
Assertion with `==` failed.

left: 1
right: 2
"""

Your solution should work with the ==, >, <, <=, >=, and === operators.

Print a "Success" message if the assertion passes.

Example Solution

If we want to have full control over the result, one solution would be to use multiple function heads (or any means of control flow) for each operator. However, if we don’t have custom messages for each operator, we can cleverly use the apply/3 function to keep our solution minimal.

defmodule CustomAssertion do
  @success "Success!"

  def check(operator, left, right) do
    if apply(Kernel, operator, [left, right]) do
      @success
    else
      """
      Assertion with #{operator} failed.
      left: #{left}
      right: #{right}
      """
    end
  end

  defmacro assert({operator, _meta, [left, right]}) do
    quote do
      CustomAssertion.check(unquote(operator), unquote(left), unquote(right))
    end
  end
end

defmodule CustomAssertion do
  defmacro assert({operator, _meta, [left, right]}) do
  end
end

Your solution should be able to display failure messages for the following assertions.

require CustomAssertion

CustomAssertion.assert(1 == 2) |> IO.puts()
CustomAssertion.assert(1 === 2) |> IO.puts()
CustomAssertion.assert(1 > 2) |> IO.puts()
CustomAssertion.assert(1 >= 2) |> IO.puts()
CustomAssertion.assert(2 < 1) |> IO.puts()
CustomAssertion.assert(2 <= 1) |> IO.puts()

Your solution should display success messages for the following assertions.

require CustomAssertion

CustomAssertion.assert(1 == 1) |> IO.puts()
CustomAssertion.assert(1 === 1) |> IO.puts()
CustomAssertion.assert(2 > 1) |> IO.puts()
CustomAssertion.assert(1 >= 1) |> IO.puts()
CustomAssertion.assert(1 < 2) |> IO.puts()
CustomAssertion.assert(1 <= 1) |> IO.puts()

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "custom_assertions_reading"
    "exercises" -> "custom_assertions_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b custom-assertions-exercise
$ git add .
$ git commit -m "finish custom assertions exercise"
$ git push origin custom-assertions-exercise

Create a pull request from your custom-assertions-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

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