Add several elixir solutions

elixir/grains/test/grains_test.exs

@@ -0,0 +1,61 @@
+defmodule GrainsTest do
+  use ExUnit.Case
+
+  # @tag :pending
+  test "square 1" do
+    assert Grains.square(1) === {:ok, 1}
+  end
+
+  @tag :pending
+  test "square 2" do
+    assert Grains.square(2) === {:ok, 2}
+  end
+
+  @tag :pending
+  test "square 3" do
+    assert Grains.square(3) === {:ok, 4}
+  end
+
+  @tag :pending
+  test "square 4" do
+    assert Grains.square(4) === {:ok, 8}
+  end
+
+  @tag :pending
+  test "square 16" do
+    assert Grains.square(16) === {:ok, 32768}
+  end
+
+  @tag :pending
+  test "square 32" do
+    assert Grains.square(32) === {:ok, 2_147_483_648}
+  end
+
+  @tag :pending
+  test "square 64" do
+    assert Grains.square(64) === {:ok, 9_223_372_036_854_775_808}
+  end
+
+  @tag :pending
+  test "total grains" do
+    assert Grains.total() === {:ok, 18_446_744_073_709_551_615}
+  end
+
+  @tag :pending
+  test "square greater than 64 returns an error" do
+    assert Grains.square(65) ===
+             {:error, "The requested square must be between 1 and 64 (inclusive)"}
+  end
+
+  @tag :pending
+  test "negative square returns an error" do
+    assert Grains.square(-1) ===
+             {:error, "The requested square must be between 1 and 64 (inclusive)"}
+  end
+
+  @tag :pending
+  test "square 0 returns an error" do
+    assert Grains.square(0) ===
+             {:error, "The requested square must be between 1 and 64 (inclusive)"}
+  end
+end

elixir/grains/test/test_helper.exs

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+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true)