rewrite error module

Author: woylie

lib/tds/error.ex

@@ -1,12 +1,55 @@
 defmodule Tds.Error do
+  @moduledoc """
+  Defines the `Tds.Error` struct.
+
+  The struct has to fields:
+
+  * `:message`: expected to be a string
+  * `:mssql`: expected to be a keyword list with the fields `line_number`,
+              `number` and `msg_text`
+
+  ## Usage
+
+      iex> raise Tds.Error
+      ** (Tds.Error) An error occured.
+
+      iex> raise Tds.Error, "some error"
+      ** (Tds.Error) some error
+
+      iex> raise Tds.Error, "some error"
+      ** (Tds.Error) some error
+
+      iex> raise Tds.Error, line_number: 10, number: 8, msg_text: "some error"
+      ** (Tds.Error) Line 10 (8): some error
+  """
+
   defexception [:message, :mssql]
 
-  def message(e) do
-    msg =
-    if kw = e.mssql do
-      "#{kw[:line_number]} (#{kw[:number]}): #{kw[:msg_text]}"
-    end
+  @spec exception(String.t() | keyword) :: %__MODULE__{}
+  def exception(message) when is_binary(message) do
+    %__MODULE__{message: message}
+  end
+
+  def exception(line_number: line_number, number: number, msg_text: msg) do
+    %__MODULE__{
+      mssql: %{
+        line_number: line_number,
+        number: number,
+        msg_text: msg
+      }
+    }
+  end
+
+  def exception(_) do
+    %__MODULE__{message: "An error occured."}
+  end
+
+  @spec message(%__MODULE__{}) :: String.t()
+  def message(%__MODULE__{mssql: mssql}) when is_map(mssql) do
+    "Line #{mssql[:line_number]} (#{mssql[:number]}): #{mssql[:msg_text]}"
+  end
 
-    msg || e.message
+  def message(%__MODULE__{message: message}) when is_binary(message) do
+    message
   end
 end

test/error_test.exs

@@ -0,0 +1,27 @@
+defmodule ErrorTest do
+  use ExUnit.Case, async: true
+
+  test "raises a Tds.Error with a string message" do
+    assert_raise Tds.Error, "Some wild error.", fn ->
+      raise Tds.Error, "Some wild error."
+    end
+  end
+
+  test "raises a Tds.Error with Mssql infos" do
+    assert_raise Tds.Error, "Line 4 (8): something bad", fn ->
+      raise Tds.Error, line_number: 4, number: 8, msg_text: "something bad"
+    end
+  end
+
+  test "raises a Tds.Error with a default message as a fallback" do
+    # no arguments
+    assert_raise Tds.Error, "An error occured.", fn ->
+      raise Tds.Error
+    end
+
+    # weird arguments
+    assert_raise Tds.Error, "An error occured.", fn ->
+      raise Tds.Error, profession: "crocodile hunter"
+    end
+  end
+end