Add option parser and tests for it

TESTS!!!!

issues/lib/issues/cli.ex

@@ -0,0 +1,34 @@
+defmodule Issues.CLI do
+  @default_count 4
+
+  @moduledoc """
+  Handle the command line parsing and the dispatch to the various functions that end up
+  generating a table of the last _n_ issues in a github project.
+  """
+
+  def run(argv) do
+    parse_args(argv)
+  end
+
+  def parse_args(argv) do
+    parse =
+      OptionParser.parse(argv,
+        switches: [help: :boolean],
+        aliases: [h: :help]
+      )
+
+    case parse do
+      {[help: true], _, _} ->
+        :help
+
+      {_, [user, project, count], _} ->
+        {user, project, String.to_integer(count)}
+
+      {_, [user, project], _} ->
+        {user, project, @default_count}
+
+      _ ->
+        :help
+    end
+  end
+end

issues/test/cli_test.exs

@@ -0,0 +1,19 @@
+defmodule CliTest do
+  use ExUnit.Case
+  doctest Issues
+
+  import Issues.CLI, only: [parse_args: 1]
+
+  test ":help returned by option parsing the -h and --help options" do
+    assert parse_args(["-h", "anything"]) == :help
+    assert parse_args(["--help", "anything"]) == :help
+  end
+
+  test "three values returned if three given" do
+    assert parse_args(["user", "project", "99"]) == {"user", "project", 99}
+  end
+
+  test "two values and default count returned if two values given" do
+    assert parse_args(["user", "project"]) == {"user", "project", 4}
+  end
+end