Add collision/merge with bottom

lib/bottom.ex

@@ -0,0 +1,18 @@
+defmodule Tetris.Bottom do
+  def merge(bottom, points) do
+    points
+    |> Enum.map( fn {x, y, c} -> {{x, y }, {x, y, c}} end)
+    |> Enum.into(bottom)
+  end
+
+  def collides?(bottom, {x,y, _colour}) do
+    collides?(bottom, {x,y})
+  end
+  def collides?(bottom, {x,y}) do
+    !!Map.get(bottom, {x,y})
+  end
+  def collides?(bottom, points) when is_list(points) do
+    Enum.any?(points, &collides?(bottom,&1))
+  end
+
+end

lib/points.ex

@@ -1,6 +1,6 @@
 defmodule Tetris.Points do
 
-  def move_to_location(points, {x,y}=_location) do
+  def move_to_location(points, {x,y}) do
     Enum.map(points,fn {dx, dy} -> {dx + x, dy + y} end )
   end
 

test/bottom_test.exs

@@ -0,0 +1,29 @@
+defmodule BottomTest do
+  use ExUnit.Case
+  import Tetris.Bottom
+
+
+  test "Various Collisions" do
+    bottom = %{{1,1} => {1,1, :blue}}
+
+    assert collides? bottom, {1,1}
+    refute collides? bottom, {1,2}
+    assert collides? bottom, {1,1, :red}
+    assert collides? bottom, {1,1, :blue}
+    refute collides? bottom, {1,2, :red}
+
+    assert collides? bottom, [{1,2, :red}, {1,1, :red}]
+    refute collides? bottom, [{3,2, :blue}, {4,4, :red}]
+  end
+
+  test "test simple merge with bottom" do
+    bottom = %{{1,1} => {1,1, :blue}}
+    actual = merge bottom, [{1,2, :red}, {1,3, :red}]
+    expected = %{
+      {1,1} => {1, 1, :blue},
+      {1,2} => {1, 2, :red},
+      {1,3} => {1, 3, :red}
+    }
+    assert actual == expected
+  end
+end