A few simple koans about agents

lib/koans/14_agents.ex

@@ -0,0 +1,36 @@
+defmodule Agents do
+  use Koans
+
+  koan "Agents maintain state, so you can ask them about it" do
+    Agent.start_link(fn() -> "Hi there" end, name: __MODULE__)
+    assert Agent.get(__MODULE__, &(&1)) == :__
+  end
+
+  koan "Update to update the state" do
+    Agent.start_link(fn() -> "Hi there" end, name: __MODULE__)
+
+    Agent.update(__MODULE__, fn(old) ->
+      String.upcase(old)
+    end)
+    assert Agent.get(__MODULE__, &(&1)) == :__
+  end
+
+  koan "Use get_and_update when you need read and change a value in one go" do
+    Agent.start_link(fn() -> ["Milk"] end, name: __MODULE__)
+
+    old_list = Agent.get_and_update(__MODULE__, fn(old) ->
+      {old, ["Bread" | old]}
+    end)
+
+    assert old_list == :__
+    assert Agent.get(__MODULE__, &(&1)) == :__
+  end
+
+  koan "Somebody has to switch off the light at the end of the day" do
+    Agent.start_link(fn() -> ["Milk"] end, name: __MODULE__)
+
+    result = Agent.stop(__MODULE__)
+
+    assert result == :__
+  end
+end

lib/runner.ex

@@ -12,6 +12,7 @@ defmodule Runner do
     Enums,
     Processes,
     Tasks,
+    Agents,
   ]
 
   def koan?(koan), do: Enum.member?(@modules, koan)

test/koans_harness_test.exs

@@ -222,6 +222,17 @@ defmodule KoansHarnessTest do
     test_all(Tasks, answers)
   end
 
+  test "Agents" do
+    answers = [
+      "Hi there",
+      "HI THERE",
+      {:multiple, [["Milk"], ["Bread", "Milk"]]},
+      :ok,
+    ]
+
+    test_all(Agents, answers)
+  end
+
   def test_all(module, answers) do
     module.all_koans
     |> Enum.zip(answers)