Custom Assertions

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.9", 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()

Commit Your Progress

DockYard Academy now recommends you use the latest Release rather than forking or cloning our repository.

Run git status to ensure there are no undesirable changes. Then run the following in your command line from the curriculum folder to commit your progress.

$ git add .
$ git commit -m "finish Custom Assertions exercise"
$ git push

We’re proud to offer our open-source curriculum free of charge for anyone to learn from at their own pace.

We also offer a paid course where you can learn from an instructor alongside a cohort of your peers. We will accept applications for the June-August 2023 cohort soon.

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