diff --git a/test/excache/introspection_test.exs b/test/excache/introspection_test.exs
index 070d773..e6d41ee 100644
--- a/test/excache/introspection_test.exs
+++ b/test/excache/introspection_test.exs
@@ -467,3 +467,160 @@ defmodule Excache.IntrospectionTest do
                Client.command(conn, ["LINSERT", "a", "BEFORE", "b"])
     end
 
+    test "GETKEYS walks plain ranges" do
+      assert getkeys(["GET", "one"]) == ["one"]
+      assert getkeys(["MSET", "a", "1", "b", "2", "c", "3"]) == ["a", "b", "c"]
+      assert getkeys(["DEL", "a", "b", "c"]) == ["a", "b", "c"]
+      assert getkeys(["BLPOP", "left", "right", "0"]) == ["left", "right"]
+      assert getkeys(["BITOP", "AND", "dest", "src1", "src2"]) == ["dest", "src1", "src2"]
+      assert getkeys(["SMOVE", "from", "to", "member"]) == ["from", "to"]
+      assert getkeys(["EXPIRE", "solo", "10"]) == ["solo"]
+    end
+
+    test "GETKEYS resolves the commands whose keys move" do
+      assert getkeys(["XREAD", "COUNT", "2", "STREAMS", "s1", "s2", "0", "0"]) == ["s1", "s2"]
+
+      assert getkeys([
+               "XREADGROUP",
+               "GROUP",
+               "g",
+               "c",
+               "STREAMS",
+               "stream",
+               ">"
+             ]) == ["stream"]
+
+      assert getkeys(["SINTERCARD", "2", "a", "b", "LIMIT", "1"]) == ["a", "b"]
+      assert getkeys(["BLMPOP", "0", "2", "a", "b", "LEFT"]) == ["a", "b"]
+      assert getkeys(["OBJECT", "ENCODING", "thing"]) == ["thing"]
+      assert getkeys(["MEMORY", "USAGE", "thing"]) == ["thing"]
+      assert getkeys(["XINFO", "STREAM", "events"]) == ["events"]
+      assert getkeys(["XGROUP", "CREATE", "events", "group", "$"]) == ["events"]
+    end
+
+    test "GETKEYS refuses what it cannot answer" do
+      assert getkeys(["PING"]) == {:error, "ERR The command has no key arguments"}
+      assert getkeys(["MEMORY", "DOCTOR"]) == {:error, "ERR The command has no key arguments"}
+      assert getkeys(["NOSUCHCOMMAND", "a"]) == {:error, "ERR Invalid command specified"}
+
+      assert getkeys(["GET"]) ==
+               {:error, "ERR Invalid number of arguments specified for command"}
+
+      assert getkeys(["XREAD", "COUNT", "2", "s1", "0"]) ==
+               {:error, "ERR Invalid arguments specified for command"}
+
+      assert getkeys(["SINTERCARD", "3", "a", "b"]) ==
+               {:error, "ERR Invalid arguments specified for command"}
+    end
+
+    test "DOCS answers with the group and arity taken from the same table" do
+      assert {[{:array, entries}], _state} =
+               Introspection.dispatch(
+                 "COMMAND",
+                 ["DOCS", "zadd", "nosuchcommand"],
+                 commandState()
+               )
+
+      assert entries == [
+               {:bulk, "zadd"},
+               {:array, [{:bulk, "group"}, {:bulk, "zset"}, {:bulk, "arity"}, {:integer, -4}]}
+             ]
+
+      assert {[{:array, everything}], _state} =
+               Introspection.dispatch("COMMAND", ["DOCS"], commandState())
+
+      assert length(everything) == 2 * length(Enum.uniq(Command.known_commands()))
+    end
+
+    test "an unknown subcommand is named in the error" do
+      assert {[{:error, message}], _state} =
+               Introspection.dispatch("COMMAND", ["NOPE"], commandState())
+
+      assert message =~ "Unknown subcommand or wrong number of arguments for 'NOPE'"
+    end
+
+    test "the extended dispatcher already routes COMMAND to this module" do
+      assert {[{:integer, count}], _state} =
+               Excache.Command.Extended.dispatch("COMMAND", ["COUNT"], commandState())
+
+      assert count == Catalog.count()
+    end
+  end
+
+  defp commandState,
+    do: Map.put(Transaction.initial_state(), :subscriptions, MapSet.new())
+
+  defp commandInfo(name) do
+    assert {[{:array, [{:array, entry}]}], _state} =
+             Introspection.dispatch("COMMAND", ["INFO", name], commandState())
+
+    [
+      {:bulk, lowered},
+      {:integer, arity},
+      {:array, flags},
+      {:integer, first},
+      {:integer, last},
+      {:integer, step}
+    ] = entry
+
+    {lowered, arity, Enum.map(flags, fn {:simple, flag} -> flag end), first, last, step}
+  end
+
+  defp getkeys(argv) do
+    case Introspection.dispatch("COMMAND", ["GETKEYS" | argv], commandState()) do
+      {[{:array, keys}], _state} -> Enum.map(keys, fn {:bulk, key} -> key end)
+      {[error], _state} -> error
+    end
+  end
+
+  defp clientField(conn, name) do
+    {text, _conn} = Client.command(conn, ["INFO", "clients"])
+    String.to_integer(fields(text)[name])
+  end
+
+  defp sections(text) do
+    for "# " <> title <- String.split(text, "\r\n"), do: title
+  end
+
+  defp fields(text) do
+    text
+    |> String.split("\r\n")
+    |> Enum.reject(fn line -> line == "" or String.starts_with?(line, "#") end)
+    |> Map.new(fn line ->
+      [key, value] = String.split(line, ":", parts: 2)
+      {key, value}
+    end)
+  end
+
+  defp listLines(text) do
+    text
+    |> String.split("\n")
+    |> Enum.reject(&(&1 == ""))
+    |> Map.new(fn line ->
+      parsed =
+        Map.new(String.split(line, " "), fn pair ->
+          [key, value] = String.split(pair, "=", parts: 2)
+          {key, value}
+        end)
+
+      {String.to_integer(parsed["id"]), parsed}
+    end)
+  end
+
+  defp blockingTask(port, args) do
+    Task.async(fn ->
+      client = Client.connect(port)
+      {reply, _client} = Client.command(client, args)
+      Client.close(client)
+      reply
+    end)
+  end
+
+  defp awaitUntil(check, attempts \\ 200) do
+    cond do
+      check.() -> :ok
+      attempts == 0 -> flunk("condition never held")
+      true -> Process.sleep(10) && awaitUntil(check, attempts - 1)
+    end
+  end
+end