Elixir ExUnit Error Fix

The Hook

You will learn how to fix common exunit errors. This matters because understanding this concept is essential for productive development. Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro.

Quick Fix

ExUnit tests

The wrong approach and the correct fix are shown below:

Wrong:

defmodule MyTest do
  use ExUnit.Case
  test "truth" do
    assert 1 + 1 == 2
  end
end

Output:

Right:

defmodule MyTest do
  use ExUnit.Case
  test "truth" do
    assert 1 + 1 == 2
    refute 1 + 1 == 3
    assert_raise ArithmeticError, fn -> 1 / 0 end
  end
  describe "group" do
    test "nested" do
      assert true
    end
  end
end

Output:

Prevention

ExUnit is built-in test framework. assert, refute, assert_raise. describe for grouping.

Common Mistakes with exunit

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world ELIXIR code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ