ExUnit

Review Questions

• Are there any questions?

• Are there any topics we would like to go over again?

• Are there any questions about previous exercises?

ExUnit

Discussion Prompts

• What should we test?
• What are the benefits of testing?
• How do we want to handle and test errors?

Example: Writing a basic test

defmodule Math do
  def double(integer) do
    integer * 2
  end
end

ExUnit.start(auto_run: false)

defmodule MathTest do
  use ExUnit.Case

  test "double/1 input" do
    # Example based testing
    assert Math.double(2) == 4
    assert Math.double(4) == 8
  end

  # similarities
  # pro: highly robust
  # con: smart
  # differences
  # randomization: more performant -> false positives (flakey)
  # limited set of cases -> less performant -> slower
  test "randomization" do
    # 2
    random_integer = Enum.random(1..100)
    assert Math.double(random_integer) == random_integer * 2
  end

  test "include a range of test cases" do
    Enum.each(1..100, fn integer ->
      assert Math.double(integer) == integer * 2
    end)
  end
end

ExUnit.run()

Example: Happy Path vs Edge Cases

flowchart LR
input --> double/1 --> output
i0[2] --> d0[double/1] --> o2[4]
i1[-2] --> d1[double/1] --> o1[-4]

Edge case

• “2” -> double/1 -> error

defmodule Math do
  # Happy Path
  def double(integer) when is_integer(integer) do
    integer * 2
  end

  # Edge Cases
  def double(integer) when is_integer(integer) and integer < 0 do
    {:error, :negative_numbers_not_valid}
  end

  def double(integer) do
    {:error, :invalid_input}
  end
end

ExUnit.start(auto_run: false)

defmodule MathTest do
  use ExUnit.Case

  test "double/1 positive integers" do
    # Example based testing
    assert Math.double(2) == 4
    assert Math.double(4) == 8
  end

  test "double/1 negative integers" do
    assert Math.double(-2) == {:error, :negative_numbers_not_valid}
  end

  test "double/1 string integer" do
    assert Math.double("2") == {:error, :invalid_input}
  end
end

ExUnit.run()

Exercises

The teacher will provide an explanation of each exercise.

• Any questions about the exercises?

Git Merging

flowchart LR
Branch1[Branch main]
Branch2[Branch solutions]

Branch1 -- git merge main --> Branch2
Branch2 -- git merge solutions --> Branch1

style Branch2 fill:lightgreen

1. start on main
2. git checkout -b exercise (stage and commit)
3. git push -u origin exercise
4. make PR
5. git status (ensure there are no changes)
6. git checkout main (go back to main an start from step 1)

High Level Skills

1. Where am I?
2. Where do I want to go?
3. How do I get there? (git merge git push git checkout git add git commit git pull)

Where am I

• branch? (git status)
• any changes? (unstaged, staged, commits?) If so, what are they? (check the source control tab)

Where do I want to go

• Am I trying to commit some changes?
• Am I satisfied with the current changes? (check the source control tab)
• Am I trying to commit? Am I trying to make a pull request?
• Am I trying to get some update?

I want an update

1. sync
2. makes sure you are “clean” and on main
3. git pull

Go to exercise branch

1. make sure you are on main and updated
2. git checkout branchname

Update exercise branch

• maybe don’t

1. make sure main is updated
2. make sure we are on the desired (exercise) branch to update
3. git merge main
4. deal with merge conflics if present (check the source control tab) make sure nothing was overrwritten.

• you made I change (10am)
• I made a change (11am)

My change is later, and therefore more “accurate” so my change wins. Your change gets overwritten.

map1 = %{one: 1}
map2 = %{two: 2}

Map.merge(map1, map2)

map1 = %{one: 1}
map2 = %{one: 2}

Map.merge(map1, map2)