Asserting exceptions

Use assert_raise to test if an exception was raised. assert_raise takes in an Exception and a function to be executed.

  test "invalid block size" do
    assert_raise(MerkleTree.ArgumentError, (fn() -> MerkleTree.new ["a", "b", "c"] end))
  end

As you can see, you can wrap any code you want to test in an anonymous function and pass it to assert_raise.