diff --git a/.gitignore b/.gitignore
index 023d19a..a52ec8a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,4 @@ erl_crash.dump
 *.ez
 *.swp
 *.swo
+rename-*.tar
diff --git a/config/config.exs b/config/config.exs
index d2d855e..68457de 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -1 +1,3 @@
-use Mix.Config
+import Config
+
+import_config("#{Mix.env()}.exs")
diff --git a/config/dev.exs b/config/dev.exs
new file mode 100644
index 0000000..e69de29
diff --git a/config/prod.exs b/config/prod.exs
new file mode 100644
index 0000000..e69de29
diff --git a/config/test.exs b/config/test.exs
new file mode 100644
index 0000000..57aaa2b
--- /dev/null
+++ b/config/test.exs
@@ -0,0 +1,3 @@
+import Config
+
+config :rename, Rename.Repo, foo: :bar
diff --git a/lib/mix/tasks/rename.ex b/lib/mix/tasks/rename.ex
index 8315524..d24cd7b 100644
--- a/lib/mix/tasks/rename.ex
+++ b/lib/mix/tasks/rename.ex
@@ -2,42 +2,46 @@ defmodule Mix.Tasks.Rename do
   use Mix.Task
 
   def run(args \\ [])
-  def run([old_name, new_name, old_otp, new_otp | extra_options]) do
+
+  def run([old_name, new_name, old_otp, new_otp | options]) do
+    {options, _argv, _errors} =
+      options
+      |> OptionParser.parse(
+        strict: [
+          ignore_directories: :keep,
+          ignore_files: :keep,
+          starting_directory: :string,
+          include_extensions: :keep,
+          include_files: :keep
+        ]
+      )
+
+    options =
+      options
+      |> Enum.group_by(fn {k, _v} -> k end, fn {_k, v} -> v end)
+      |> Map.to_list()
+      |> maybe_put_starting_directory(Keyword.get(options, :starting_directory))
+
     Rename.run(
-      {old_name, new_name}, 
-      {old_otp, new_otp}, 
-      run_options(extra_options)
+      {old_name, new_name},
+      {old_otp, new_otp},
+      options
     )
   end
+
   def run(_bad_args) do
-    IO.puts """
+    IO.puts("""
     Did not provide required app and otp names
     Call should look like:
       mix rename OldName NewName old_name NewName
-    """
+    """)
+
     {:error, :bad_params}
   end
 
-  def run_options(extra_options, options \\ [])
-  def run_options([], options) do
-    ignore_files = options[:ignore_files] || []
-    options
-    |> Enum.reject(fn {key, _val} -> key == :ignore_files end)
-    |> Enum.concat([ignore_files: ignore_files])
-  end
-  def run_options([key, val | rest], options) do
-    rest
-    |> run_options(
-      options
-      |> Enum.concat([{parsed_key(key), val}])
-    )
-  end
+  defp maybe_put_starting_directory(options, nil), do: options
 
-  def parsed_key(key) do
-    key
-    |> String.slice(2..-1)
-    |> String.replace("-", "_")
-    |> String.to_atom
+  defp maybe_put_starting_directory(options, starting_directory) do
+    Keyword.put(options, :starting_directory, starting_directory)
   end
-
 end
diff --git a/lib/rename.ex b/lib/rename.ex
index 9d5d2e9..448d8ad 100644
--- a/lib/rename.ex
+++ b/lib/rename.ex
@@ -1,5 +1,4 @@
 defmodule Rename do
-
   @moduledoc """
   The single module that does all the renaming
   Talk about pressure
@@ -9,91 +8,148 @@ defmodule Rename do
   So it's fine
   If you're mad about it, submit a PR.
   """
+  @default_extensions ~w(
+    .ex
+    .exs
+    .eex
+    .md
+  )
 
-  @default_extensions [
-    "ex",
-    "exs",
-    "eex",
-    "md",
-  ]
-
-  @default_ignore_directories [
-    "_build",
-    "deps",
-    "assets",
-  ]
+  @default_ignore_directories ~w(
+    .elixir_ls
+    _build
+    deps
+    assets
+  )
 
   @default_starting_directory "."
 
   @default_ignore_files []
 
+  @default_include_files ~w(
+    mix.exs
+  )
+
   @doc """
   The public function you use to rename your app.
   Call looks like: run({"OldName", "NewName"}, {"old_otp", "new_otp"}, options)
   """
 
-  def run(names, opts, options \\ [])
-  def run(names = {_old_name, _new_name}, otps = {_old_otp, _new_otp}, options) do
+  def run(names, otps, options \\ [])
+
+  def run({_old_name, _new_name} = names, {_old_otp, _new_otp} = otps, options) do
+    options =
+      options
+      |> Enum.reduce(defaults(), fn
+        {key, val}, acc when is_list(val) ->
+          Keyword.put(acc, key, merge_with_default({key, val}, acc))
+
+        {k, v}, acc ->
+          Keyword.put(acc, k, v)
+      end)
+
     names
     |> rename_in_directory(
       otps,
-      options[:starting_directory] || @default_starting_directory,
+      options[:starting_directory],
       options
     )
   end
 
   def run(_names, _otp, _options), do: {:error, "bad params"}
 
+  defp defaults do
+    [
+      ignore_directories: @default_ignore_directories,
+      ignore_files: @default_ignore_files,
+      include_extensions: @default_extensions,
+      starting_directory: @default_starting_directory,
+      include_files: @default_include_files
+    ]
+  end
+
   defp rename_in_directory(names = {old_name, new_name}, otps = {old_otp, new_otp}, cwd, options) do
     cwd
-    |> File.ls!
-    |> Enum.each(fn path ->
-      file_or_dir = cwd <> "/" <> path
+    |> File.ls!()
+    |> Enum.reject(&ignored_directory?(&1, options))
+    |> Enum.each(fn file_or_dir ->
+      path = Path.join([cwd, file_or_dir])
+
       cond do
-        is_valid_directory?(file_or_dir, options) ->
-          rename_in_directory(names, otps, file_or_dir, options)
+        File.dir?(path) ->
+          rename_in_directory(names, otps, path, options)
           true
-        is_valid_file?(file_or_dir, options) ->
-          file_or_dir
-          |> File.read
+
+        is_valid_file?(path, options) ->
+          path
+          |> File.read()
           |> case do
-            {:ok, file} -> 
-              updated_file = file
-              |> String.replace(old_name, new_name)
-              |> String.replace(old_otp, new_otp)
-              File.write(file_or_dir, updated_file)
+            {:ok, file} ->
+              updated_file =
+                file
+                |> String.replace(old_name, new_name)
+                |> String.replace(old_otp, new_otp)
+                |> String.replace(dasherised(old_otp), dasherised(new_otp))
+
+              File.write(path, updated_file)
               true
+
             _ ->
               false
           end
-        true -> 
+
+        true ->
           false
       end
       |> case do
-        true -> 
-          file_or_dir
-          |> File.rename(String.replace(file_or_dir, old_otp, new_otp))
-        _ -> :nothing
+        true ->
+          rename_file(path, old_otp, new_otp)
+
+        _ ->
+          :ok
       end
     end)
   end
 
-  defp is_valid_directory?(dir, options) do
-    File.dir?(dir) and
-    dir in (options[:ignore_directories] || @default_ignore_directories) == false
+  defp rename_file(path, old_otp, new_otp) do
+    File.rename(path, String.replace(path, old_otp, new_otp))
+  end
+
+  defp ignored_directory?(dir, options) do
+    File.dir?(dir) and dir in options[:ignore_directories]
   end
 
   defp is_valid_file?(file, options) do
-    File.exists?(file) and
-    file in (options[:ignore_files] || @default_ignore_files) == false and
-    has_valid_extension?(file, options)
+    File.exists?(file) &&
+      has_valid_extension?(file, options) &&
+      (include?(file, options) || !ignore?(file, options))
+  end
+
+  def include?(file, options) do
+    Path.basename(file) in options[:include_files]
+  end
+
+  def ignore?(file, options) do
+    Path.basename(file) in options[:ignore_files]
   end
 
   defp has_valid_extension?(file, options) do
-    extension = file
-    |> String.split(".")
-    |> List.last
-    extension in (options[:valid_extensions] || @default_extensions)
+    file
+    |> Path.extname()
+    |> case do
+      "" ->
+        true
+
+      ext ->
+        ext in options[:include_extensions]
+    end
   end
 
+  defp dasherised(name), do: String.replace(name, "_", "-")
+
+  defp merge_with_default({key, val}, acc) do
+    acc
+    |> Keyword.get(key)
+    |> then(&(&1 ++ val))
+  end
 end
diff --git a/lib/rename/.keep b/lib/rename/.keep
new file mode 100644
index 0000000..e69de29
diff --git a/mix.exs b/mix.exs
index 1d49e1c..1bbe038 100644
--- a/mix.exs
+++ b/mix.exs
@@ -6,17 +6,18 @@ defmodule Rename.Mixfile do
       app: :rename,
       version: "0.1.0",
       elixir: "~> 1.4",
-      build_embedded: Mix.env == :prod,
-      start_permanent: Mix.env == :prod,
+      build_embedded: Mix.env() == :prod,
+      start_permanent: Mix.env() == :prod,
       description: description(),
+      elixirc_paths: elixirc_paths(Mix.env()),
       package: package(),
       deps: deps(),
       test_coverage: [tool: ExCoveralls],
       preferred_cli_env: [
-        "coveralls": :test, 
+        coveralls: :test,
         "coveralls.detail": :test,
         "coveralls.post": :test,
-        "coveralls.html": :test,
+        "coveralls.html": :test
       ]
     ]
   end
@@ -38,8 +39,10 @@ defmodule Rename.Mixfile do
   defp deps do
     [
       {:excoveralls, "~> 0.6", only: :test},
-      {:ex_doc,      ">= 0.0.0", only: :dev},
+      {:ex_doc, ">= 0.0.0", only: :dev}
     ]
   end
 
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
+  defp elixirc_paths(_), do: ["lib"]
 end
diff --git a/mix.lock b/mix.lock
index 4e8d949..bb5b5ff 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,11 +1,13 @@
-%{"certifi": {:hex, :certifi, "1.0.0", "1c787a85b1855ba354f0b8920392c19aa1d06b0ee1362f9141279620a5be2039", [:rebar3], []},
-  "earmark": {:hex, :earmark, "1.2.0", "bf1ce17aea43ab62f6943b97bd6e3dc032ce45d4f787504e3adf738e54b42f3a", [:mix], []},
-  "ex_doc": {:hex, :ex_doc, "0.15.0", "e73333785eef3488cf9144a6e847d3d647e67d02bd6fdac500687854dd5c599f", [:mix], [{:earmark, "~> 1.1", [hex: :earmark, optional: false]}]},
-  "excoveralls": {:hex, :excoveralls, "0.6.3", "894bf9254890a4aac1d1165da08145a72700ff42d8cb6ce8195a584cb2a4b374", [:mix], [{:exjsx, "~> 3.0", [hex: :exjsx, optional: false]}, {:hackney, ">= 0.12.0", [hex: :hackney, optional: false]}]},
-  "exjsx": {:hex, :exjsx, "3.2.1", "1bc5bf1e4fd249104178f0885030bcd75a4526f4d2a1e976f4b428d347614f0f", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, optional: false]}]},
-  "hackney": {:hex, :hackney, "1.7.1", "e238c52c5df3c3b16ce613d3a51c7220a784d734879b1e231c9babd433ac1cb4", [:rebar3], [{:certifi, "1.0.0", [hex: :certifi, optional: false]}, {:idna, "4.0.0", [hex: :idna, optional: false]}, {:metrics, "1.0.1", [hex: :metrics, optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, optional: false]}, {:ssl_verify_fun, "1.1.1", [hex: :ssl_verify_fun, optional: false]}]},
-  "idna": {:hex, :idna, "4.0.0", "10aaa9f79d0b12cf0def53038547855b91144f1bfcc0ec73494f38bb7b9c4961", [:rebar3], []},
-  "jsx": {:hex, :jsx, "2.8.2", "7acc7d785b5abe8a6e9adbde926a24e481f29956dd8b4df49e3e4e7bcc92a018", [:mix, :rebar3], []},
-  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], []},
-  "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], []},
-  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.1", "28a4d65b7f59893bc2c7de786dec1e1555bd742d336043fe644ae956c3497fbe", [:make, :rebar], []}}
+%{
+  "certifi": {:hex, :certifi, "1.0.0", "1c787a85b1855ba354f0b8920392c19aa1d06b0ee1362f9141279620a5be2039", [:rebar3], [], "hexpm", "44a5aa4261490a7d7fa6909ab4bcf14bff928a4fef49e80fc1e7a8fdb7b45f79"},
+  "earmark": {:hex, :earmark, "1.2.0", "bf1ce17aea43ab62f6943b97bd6e3dc032ce45d4f787504e3adf738e54b42f3a", [:mix], [], "hexpm", "6709251dd10e70cca0d50be8a25adc38c701b39eac2da3b1c166e3e7e4d358ed"},
+  "ex_doc": {:hex, :ex_doc, "0.15.0", "e73333785eef3488cf9144a6e847d3d647e67d02bd6fdac500687854dd5c599f", [:mix], [{:earmark, "~> 1.1", [hex: :earmark, repo: "hexpm", optional: false]}], "hexpm", "e5ea59f50ecdfe4cc755808450dafe35221d5a0f4a31c42e80a7188eca570e4c"},
+  "excoveralls": {:hex, :excoveralls, "0.6.3", "894bf9254890a4aac1d1165da08145a72700ff42d8cb6ce8195a584cb2a4b374", [:mix], [{:exjsx, "~> 3.0", [hex: :exjsx, repo: "hexpm", optional: false]}, {:hackney, ">= 0.12.0", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm", "33b8e869a0afe422e2a05794ac67bed6570498173a02a80f0c88bc0fe3580287"},
+  "exjsx": {:hex, :exjsx, "3.2.1", "1bc5bf1e4fd249104178f0885030bcd75a4526f4d2a1e976f4b428d347614f0f", [:mix], [{:jsx, "~> 2.8.0", [hex: :jsx, repo: "hexpm", optional: false]}], "hexpm", "b55727b206dab96feb025267e5c122ddb448f55b6648f9156b8d481215d80290"},
+  "hackney": {:hex, :hackney, "1.7.1", "e238c52c5df3c3b16ce613d3a51c7220a784d734879b1e231c9babd433ac1cb4", [:rebar3], [{:certifi, "1.0.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "4.0.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.1", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm", "ec8309cb6d42251513492ef683d212c614d78b20594e5f4d89a05d8411dd0dea"},
+  "idna": {:hex, :idna, "4.0.0", "10aaa9f79d0b12cf0def53038547855b91144f1bfcc0ec73494f38bb7b9c4961", [:rebar3], [], "hexpm", "f1b699f7275728538da7b5e35679f9e0f41ad8e0a49896e6a27b61867ed344eb"},
+  "jsx": {:hex, :jsx, "2.8.2", "7acc7d785b5abe8a6e9adbde926a24e481f29956dd8b4df49e3e4e7bcc92a018", [:mix, :rebar3], [], "hexpm", "b4c5d3230b397c8d95579e4a3d72826bb6463160130ccf4182f5be8579b5f44c"},
+  "metrics": {:hex, :metrics, "1.0.1", "25f094dea2cda98213cecc3aeff09e940299d950904393b2a29d191c346a8486", [:rebar3], [], "hexpm", "69b09adddc4f74a40716ae54d140f93beb0fb8978d8636eaded0c31b6f099f16"},
+  "mimerl": {:hex, :mimerl, "1.0.2", "993f9b0e084083405ed8252b99460c4f0563e41729ab42d9074fd5e52439be88", [:rebar3], [], "hexpm", "7a4c8e1115a2732a67d7624e28cf6c9f30c66711a9e92928e745c255887ba465"},
+  "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.1", "28a4d65b7f59893bc2c7de786dec1e1555bd742d336043fe644ae956c3497fbe", [:make, :rebar], [], "hexpm", "4f8805eb5c8a939cf2359367cb651a3180b27dfb48444846be2613d79355d65e"},
+}
diff --git a/test/mix/tasks/rename_test.exs b/test/mix/tasks/rename_test.exs
new file mode 100644
index 0000000..3d6da38
--- /dev/null
+++ b/test/mix/tasks/rename_test.exs
@@ -0,0 +1,50 @@
+defmodule Mix.Tasks.RenameTest do
+  use Rename.UnitCase
+
+  @test_copy_dir "test_copy"
+  @old_app_name "Rename"
+  @old_app_otp "rename"
+  @new_app_name "ToDoTwitterClone"
+  @new_app_otp "to_do_twitter_clone"
+
+  describe "run/1" do
+    test "rename mix task works" do
+      create_copy_of_app(@test_copy_dir)
+
+      Mix.Tasks.Rename.run([
+        @old_app_name,
+        @new_app_name,
+        @old_app_otp,
+        @new_app_otp,
+        "--starting-directory",
+        @test_copy_dir,
+        "--ignore-directories",
+        "foo"
+      ])
+
+      mix_file = File.read!(@test_copy_dir <> "/mix.exs")
+      assert mix_file |> String.contains?(@new_app_name)
+      assert mix_file |> String.contains?(@new_app_otp)
+      assert mix_file |> String.contains?(@old_app_name) == false
+      main_module = File.read!(@test_copy_dir <> "/lib/" <> @new_app_otp <> ".ex")
+      assert main_module |> String.contains?(@new_app_name)
+      assert main_module |> String.contains?(@old_app_name) == false
+      readme = File.read!(@test_copy_dir <> "/README.md")
+      assert readme |> String.contains?(@new_app_name)
+      assert readme |> String.contains?(@new_app_otp)
+      assert readme |> String.contains?(@old_app_name) == false
+
+      delete_copy_of_app(@test_copy_dir)
+    end
+  end
+
+  test "rename mix task should give proper error for bad params" do
+    {stdout, 0} = System.cmd("mix", ["rename", "not", "enought", "params"])
+
+    assert stdout =~ """
+           Did not provide required app and otp names
+           Call should look like:
+             mix rename OldName NewName old_name NewName
+           """
+  end
+end
diff --git a/test/rename_test.exs b/test/rename_test.exs
index fa461ec..84766ba 100644
--- a/test/rename_test.exs
+++ b/test/rename_test.exs
@@ -1,94 +1,81 @@
 defmodule RenameTest do
-  use ExUnit.Case
+  use Rename.UnitCase
 
   @test_copy_dir "test_copy"
   @old_app_name "Rename"
   @old_app_otp "rename"
   @new_app_name "ToDoTwitterClone"
   @new_app_otp "to_do_twitter_clone"
-  
-  test "should properly rename app with default options" do
-    create_copy_of_app()
+
+  setup_all do
+    create_copy_of_app(@test_copy_dir)
+
     Rename.run(
-      {@old_app_name, @new_app_name}, 
-      {@old_app_otp, @new_app_otp}, 
+      {@old_app_name, @new_app_name},
+      {@old_app_otp, @new_app_otp},
       starting_directory: @test_copy_dir
     )
-    mix_file = File.read!(@test_copy_dir <> "/mix.exs")
-    assert mix_file |> String.contains?(@new_app_name)
-    assert mix_file |> String.contains?(@new_app_otp)
-    assert mix_file |> String.contains?(@old_app_name) == false
-    main_module = File.read!(@test_copy_dir <> "/lib/" <> @new_app_otp <> ".ex")
-    assert main_module |> String.contains?(@new_app_name)
-    assert main_module |> String.contains?(@old_app_name) == false
-    readme = File.read!(@test_copy_dir <> "/README.md")
-    assert readme |> String.contains?(@new_app_name)
-    assert readme |> String.contains?(@new_app_otp)
-    assert readme |> String.contains?(@old_app_name) == false
-    delete_copy_of_app()
-  end
 
-  test "should give proper error for invalid params" do
-    assert Rename.run(
-      {@old_app_name, @new_app_name}, 
-      starting_directory: @test_copy_dir
-    ) == {:error, "bad params"}
+    on_exit(fn -> delete_copy_of_app(@test_copy_dir) end)
   end
 
-  test "rename mix task works" do
-    create_copy_of_app()
-    Mix.Tasks.Rename.run([
-      @old_app_name, 
-      @new_app_name, 
-      @old_app_otp, 
-      @new_app_otp, 
-      "--starting-directory", 
-      @test_copy_dir,
-    ])
-    mix_file = File.read!(@test_copy_dir <> "/mix.exs")
-    assert mix_file |> String.contains?(@new_app_name)
-    assert mix_file |> String.contains?(@new_app_otp)
-    assert mix_file |> String.contains?(@old_app_name) == false
-    main_module = File.read!(@test_copy_dir <> "/lib/" <> @new_app_otp <> ".ex")
-    assert main_module |> String.contains?(@new_app_name)
-    assert main_module |> String.contains?(@old_app_name) == false
-    readme = File.read!(@test_copy_dir <> "/README.md")
-    assert readme |> String.contains?(@new_app_name)
-    assert readme |> String.contains?(@new_app_otp)
-    assert readme |> String.contains?(@old_app_name) == false
-    delete_copy_of_app()
-  end
+  describe "run/3" do
+    test "should rename mix file" do
+      file = File.read!(@test_copy_dir <> "/mix.exs")
 
-  test "rename mix task should give proper error for bad params" do
-    {stdout, 0} = System.cmd("mix", ["rename", "not", "enought", "params"])
-    assert stdout =~ """
-                     Did not provide required app and otp names
-                     Call should look like:
-                       mix rename OldName NewName old_name NewName
-                     """
-  end
+      assert String.contains?(file, @new_app_name)
+      assert String.contains?(file, @old_app_name) == false
+      assert String.contains?(file, @new_app_otp)
+      assert String.contains?(file, @old_app_otp) == false
+    end
 
-  defp create_copy_of_app do
-    File.mkdir(@test_copy_dir)
-    File.ls!
-    |> Enum.each(fn path -> 
-      if not_ignored_path(path) do
-        System.cmd("cp", ["-r", path, @test_copy_dir])
-      end
-    end)
-  end
+    test "should rename main module" do
+      file = File.read!(@test_copy_dir <> "/lib/" <> @new_app_otp <> ".ex")
 
-  defp delete_copy_of_app() do
-    System.cmd("rm", ["-rf", @test_copy_dir])
-  end
+      assert String.contains?(file, @new_app_name)
+      assert String.contains?(file, @old_app_name) == false
+      assert String.contains?(file, @new_app_otp)
+      assert String.contains?(file, @old_app_otp) == false
+    end
+
+    test "should rename README" do
+      file = File.read!(@test_copy_dir <> "/README.md")
+
+      assert String.contains?(file, @new_app_name)
+      assert String.contains?(file, @old_app_name) == false
+      assert String.contains?(file, @new_app_otp)
+      assert String.contains?(file, @old_app_otp) == false
+    end
+
+    test "should rename gitignore" do
+      file = File.read!(@test_copy_dir <> "/.gitignore")
+
+      assert String.contains?(file, @new_app_otp)
+      assert String.contains?(file, @old_app_otp) == false
+    end
+
+    test "should rename config" do
+      file = File.read!(@test_copy_dir <> "/config/test.exs")
+
+      assert String.contains?(file, @new_app_name)
+      assert String.contains?(file, @old_app_name) == false
+      assert String.contains?(file, @new_app_otp)
+      assert String.contains?(file, @old_app_otp) == false
+    end
+
+    test "should rename dir" do
+      assert File.dir?("#{@test_copy_dir}/lib/#{@new_app_otp}")
+    end
+
+    test "should rename tests" do
+      assert File.exists?("#{@test_copy_dir}/test/#{@new_app_otp}_test.exs")
+    end
 
-  defp not_ignored_path(path) do
-    [
-      "_build",
-      "deps", 
-      @test_copy_dir,
-      ".git",
-    ]
-    |> Enum.find(&(&1 == path)) == nil
+    test "should give proper error for invalid params" do
+      assert Rename.run(
+               {@old_app_name, @new_app_name},
+               starting_directory: @test_copy_dir
+             ) == {:error, "bad params"}
+    end
   end
 end
diff --git a/test/support/unit_case.ex b/test/support/unit_case.ex
new file mode 100644
index 0000000..979a86c
--- /dev/null
+++ b/test/support/unit_case.ex
@@ -0,0 +1,39 @@
+defmodule Rename.UnitCase do
+  @moduledoc false
+  use ExUnit.CaseTemplate
+
+  using do
+    quote do
+      import Rename.UnitCase
+    end
+  end
+
+  def create_copy_of_app(test_copy_dir) do
+    File.mkdir(test_copy_dir)
+
+    File.ls!()
+    |> Enum.filter(fn path ->
+      File.dir?(path) ||
+        Path.extname(path) in ~w(.ex .exs .md) ||
+        Path.basename(path) == ".gitignore"
+    end)
+    |> Enum.reject(&(&1 in ignored_paths(test_copy_dir)))
+    |> Enum.each(fn path ->
+      System.cmd("cp", ["-r", path, test_copy_dir])
+    end)
+  end
+
+  def delete_copy_of_app(test_copy_dir) do
+    System.cmd("rm", ["-rf", test_copy_dir])
+  end
+
+  defp ignored_paths(test_copy_dir) do
+    [
+      "_build",
+      "deps",
+      test_copy_dir,
+      ".git",
+      ".elixir_ls"
+    ]
+  end
+end