Add atom koans

lib/koans/03_atoms.ex

@@ -0,0 +1,39 @@
+defmodule Atoms do
+  use Koans
+
+  koan "Atoms are sort of like strings" do
+    adam = :human
+    assert adam == ___
+  end
+
+  koan "Strings can be converted to atoms, and vice versa" do
+    assert String.to_atom("atomized") == ___
+    assert Atom.to_string(:stringified) == ___
+  end
+
+  koan "Atoms are often used as keys, because they're faster than strings" do
+    map = %{name: "Jay"}
+    list = [name: "Jay"]
+
+    assert map[:name] == ___
+    assert list[:name] == ___
+  end
+
+  koan "It is surprising to find out that booleans are atoms" do
+    assert is_atom(true) == ___
+    assert is_atom(false) == ___
+    assert :true == ___
+    assert :false == ___
+  end
+
+  koan "Modules are also atoms" do
+    assert is_atom(String) == ___
+    assert :"Elixir.String" == ___
+    assert :"Elixir.String".upcase("hello") == ___
+  end
+
+  koan "Atoms are used to access Erlang" do
+    assert :erlang.is_list([]) == ___
+    assert :lists.sort([2, 3, 1]) == ___
+  end
+end

test/koans/atoms_koans_test.exs

@@ -0,0 +1,17 @@
+defmodule AtomsTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "Atoms" do
+    answers = [
+      :human,
+      {:multiple, [:atomized, "stringified"]},
+      {:multiple, ["Jay", "Jay"]},
+      {:multiple, [true, true, true, false]},
+      {:multiple, [true, String, "HELLO"]},
+      {:multiple, [true, [1,2,3]]},
+    ]
+
+    test_all(Atoms, answers)
+  end
+end