First attempt on Elixir location tests

test/elixir_sense/location_test.exs

@@ -0,0 +1,32 @@
+defmodule ElixirSense.LocationTest do
+  use ExUnit.Case, async: false
+
+  import ElixirSense.Location
+
+  setup do
+    elixir_src = Path.join(File.cwd!(), "/test/misc/mock_elixir_src")
+    Application.put_env(:elixir_sense, :elixir_src, elixir_src)
+
+    on_exit(fn ->
+      Application.delete_env(:elixir_sense, :elixir_src)
+    end)
+  end
+
+  describe "find_mod_fun_source/3" do
+    test "returns location of a core Elixir function" do
+      assert %ElixirSense.Location{type: :function, line: 26, column: 3, file: file} =
+               find_mod_fun_source(String, :length, 1)
+
+      assert String.ends_with?(file, "/mock_elixir_src/lib/elixir/lib/string.ex")
+    end
+  end
+
+  describe "find_type_source/3" do
+    test "returns location of a core Elixir type" do
+      assert %ElixirSense.Location{type: :typespec, line: 11, column: 3, file: file} =
+               find_type_source(String, :t, 0)
+
+      assert String.ends_with?(file, "/mock_elixir_src/lib/elixir/lib/string.ex")
+    end
+  end
+end

test/misc/mock_elixir_src/lib/elixir/lib/string.ex

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+import Kernel, except: [length: 1]
+
+defmodule String do
+  @typedoc """
+  A UTF-8 encoded binary.
+
+  The types `String.t()` and `binary()` are equivalent to analysis tools.
+  Although, for those reading the documentation, `String.t()` implies
+  it is a UTF-8 encoded binary.
+  """
+  @type t :: binary
+
+  @doc """
+  Returns the number of Unicode graphemes in a UTF-8 string.
+
+  ## Examples
+
+      iex> String.length("elixir")
+      6
+
+      iex> String.length("եոգլի")
+      5
+
+  """
+  @spec length(t) :: non_neg_integer
+  def length(string) when is_binary(string), do: length(string, 0)
+
+  defp length(gcs, acc) do
+    case :unicode_util.gc(gcs) do
+      [_ | rest] -> length(rest, acc + 1)
+      [] -> acc
+      {:error, <<_, rest::bits>>} -> length(rest, acc + 1)
+    end
+  end
+end