Add Thornwood Falls

Fixes #268

lib/magic/cards/thornwood_falls.rb

@@ -0,0 +1,19 @@
+module Magic
+  module Cards
+    ThornwoodFalls = Card("Thornwood Falls") do
+      type "Land"
+    end
+
+    class ThornwoodFalls < Card
+      def enters_tapped?
+        true
+      end
+
+      class ManaAbility < Magic::TapManaAbility
+        choices :green, :blue
+      end
+
+      def activated_abilities = [ManaAbility]
+    end
+  end
+end

spec/cards/thornwood_falls_spec.rb

@@ -0,0 +1,45 @@
+require 'spec_helper'
+
+RSpec.describe Magic::Cards::ThornwoodFalls do
+  include_context "two player game"
+
+  let(:card) { Card("Thornwood Falls") }
+
+  let!(:permanent) do
+    p1.play_land(land: card)
+    p1.permanents.by_name("Thornwood Falls").first
+  end
+
+  it "enters the battlefield tapped" do
+    game.stack.resolve!
+    expect(permanent).to be_tapped
+  end
+
+  it "has the controller gain life" do
+    expect(p1.life).to eq(21)
+  end
+
+  it "taps for green" do
+    p1.activate_mana_ability(ability: permanent.activated_abilities.first) do
+      _1.choose(:green)
+    end
+
+    expect(p1.mana_pool[:green]).to eq(1)
+  end
+
+  it "taps for blue" do
+    p1.activate_mana_ability(ability: permanent.activated_abilities.first) do
+      _1.choose(:blue)
+    end
+
+    expect(p1.mana_pool[:blue]).to eq(1)
+  end
+
+  it "cannot tap for another color" do
+    expect {
+      p1.activate_mana_ability(ability: permanent.activated_abilities.first) do
+        _1.choose(:red)
+      end
+    }.to raise_error("Invalid choice made for mana ability:")
+  end
+end