Add Dominoes exercise for Elixir track

elixir/dominoes/test/dominoes_test.exs

@@ -0,0 +1,74 @@
+defmodule DominoesTest do
+  use ExUnit.Case
+
+  test "empty input = empty output" do
+    assert Dominoes.chain?([]) == true
+  end
+
+  test "singleton input = singleton output" do
+    assert Dominoes.chain?([{1, 1}]) == true
+  end
+
+  test "singleton that can't be chained" do
+    assert Dominoes.chain?([{1, 2}]) == false
+  end
+
+  test "three elements" do
+    assert Dominoes.chain?([{1, 2}, {3, 1}, {2, 3}]) == true
+  end
+
+  test "can reverse dominoes" do
+    assert Dominoes.chain?([{1, 2}, {1, 3}, {2, 3}]) == true
+  end
+
+  test "can't be chained" do
+    assert Dominoes.chain?([{1, 2}, {4, 1}, {2, 3}]) == false
+  end
+
+  test "disconnected - double loop" do
+    assert Dominoes.chain?([{1, 2}, {2, 1}, {3, 4}, {4, 3}]) == false
+  end
+
+  test "disconnected - single isolated" do
+    assert Dominoes.chain?([{1, 2}, {2, 3}, {3, 1}, {4, 4}]) == false
+  end
+
+  test "need backtrack" do
+    # a variation in which we have to turn but no duplicates
+    assert Dominoes.chain?([{1, 2}, {2, 3}, {3, 1}, {2, 4}, {2, 4}]) == true
+  end
+
+  test "separate loops" do
+    assert Dominoes.chain?([{1, 2}, {2, 3}, {3, 1}, {1, 1}, {2, 2}, {3, 3}]) == true
+  end
+
+  test "nine elements" do
+    assert Dominoes.chain?([
+             {1, 2},
+             {5, 3},
+             {3, 1},
+             {1, 2},
+             {2, 4},
+             {1, 6},
+             {2, 3},
+             {3, 4},
+             {5, 6}
+           ]) == true
+  end
+
+  test "separate three-domino loops" do
+    refute Dominoes.chain?([{1, 2}, {2, 3}, {3, 1}, {4, 5}, {5, 6}, {6, 4}])
+  end
+
+  test "disconnected - simple" do
+    refute Dominoes.chain?([{1, 1}, {2, 2}])
+  end
+
+  test "first and last not matching" do
+    assert Dominoes.chain?([{1, 2}, {2, 3}, {3, 4}]) == false
+  end
+
+  test "wrong starting order" do
+    assert Dominoes.chain?([{2, 1}, {2, 3}, {3, 1}]) == true
+  end
+end

elixir/dominoes/test/test_helper.exs

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