Usg msg reason

lib/cli.ex

@@ -21,25 +21,34 @@ defmodule Onigumo.CLI do
             {working_dir, switches} = Keyword.pop(switches, :working_dir, File.cwd!())
 
             case switches do
-              [] -> module.main(working_dir)
-              _ -> usage_message()
+              [] ->
+                module.main(working_dir)
+
+              _ ->
+                OptionParser.to_argv(switches)
+                |> Enum.join(", ")
+                |> then(&"incompatible OPTIONS #{&1}")
+                |> usage_message()
             end
 
           :error ->
-            usage_message()
+            usage_message("invalid COMPONENT #{component}")
         end
 
-      {_, _, [_ | _]} ->
-        usage_message()
+      {_, _, invalid = [_ | _]} ->
+        Enum.map(invalid, &elem(&1, 0))
+        |> Enum.join(", ")
+        |> then(&"invalid OPTIONS #{&1}")
+        |> usage_message()
 
       {_, argv, _} when length(argv) != 1 ->
-        usage_message()
+        usage_message("exactly one COMPONENT must be provided")
     end
   end
 
-  defp usage_message() do
+  defp usage_message(reason) do
     IO.write("""
-    onigumo: invalid usage
+    onigumo: invalid usage – #{reason}
     Usage: onigumo [OPTION]... [COMPONENT]
 
     Try `onigumo --help' for more options.

test/onigumo_cli_test.exs

@@ -9,8 +9,9 @@ defmodule OnigumoCLITest do
   ]
 
   @invalid_switches [
-    "--invalid",
-    "-c"
+    ["--invalid"],
+    ["-c"],
+    ["-a", "-b"]
   ]
 
   @invalid_combinations [
@@ -32,27 +33,42 @@ defmodule OnigumoCLITest do
   describe("Onigumo.CLI.main/1") do
     for argument <- @invalid_arguments do
       test("run CLI with invalid argument #{inspect(argument)}") do
-        assert usage_message_printed?(fn -> Onigumo.CLI.main([unquote(argument)]) end)
+        assert usage_message_printed?(
+                 fn -> Onigumo.CLI.main([unquote(argument)]) end,
+                 "invalid COMPONENT #{unquote(argument)}"
+               )
       end
     end
 
     test("run CLI with no arguments") do
-      assert usage_message_printed?(fn -> Onigumo.CLI.main([]) end)
+      assert usage_message_printed?(
+               fn -> Onigumo.CLI.main([]) end,
+               "exactly one COMPONENT must be provided"
+             )
     end
 
     test("run CLI with more than one argument") do
-      assert usage_message_printed?(fn -> Onigumo.CLI.main(["Downloader", "Parser"]) end)
+      assert usage_message_printed?(
+               fn -> Onigumo.CLI.main(["Downloader", "Parser"]) end,
+               "exactly one COMPONENT must be provided"
+             )
     end
 
     for switch <- @invalid_switches do
       test("run CLI with invalid switch #{inspect(switch)}") do
-        assert usage_message_printed?(fn -> Onigumo.CLI.main([unquote(switch)]) end)
+        assert usage_message_printed?(
+                 fn -> Onigumo.CLI.main(unquote(switch)) end,
+                 "invalid OPTIONS #{Enum.join(unquote(switch), ", ")}"
+               )
       end
     end
 
     for combination <- @invalid_combinations do
       test("run CLI with invalid combination #{inspect(combination)}") do
-        assert usage_message_printed?(fn -> Onigumo.CLI.main(unquote(combination)) end)
+        assert usage_message_printed?(
+                 fn -> Onigumo.CLI.main(unquote(combination)) end,
+                 "incompatible OPTIONS --help"
+               )
       end
     end
 
@@ -73,7 +89,10 @@ defmodule OnigumoCLITest do
       end
 
       test("run CLI 'downloader' with #{inspect(switch)} without any value") do
-        assert usage_message_printed?(fn -> Onigumo.CLI.main(["downloader", unquote(switch)]) end)
+        assert usage_message_printed?(
+                 fn -> Onigumo.CLI.main(["downloader", unquote(switch)]) end,
+                 "invalid OPTIONS #{unquote(switch)}"
+               )
       end
     end
 
@@ -96,9 +115,9 @@ defmodule OnigumoCLITest do
       String.match?(output, ~r/\N\n\z/)
     end
 
-    defp usage_message_printed?(function) do
+    defp usage_message_printed?(function, reason) do
       output = capture_io(function)
-      String.starts_with?(output, "onigumo: invalid usage")
+      String.starts_with?(output, "onigumo: invalid usage – #{reason}")
     end
 
     defp help_message_printed?(function) do