Add Silent Dart

Fixes #248

lib/magic/cards/silent_dart.rb

@@ -0,0 +1,30 @@
+module Magic
+  module Cards
+    SilentDart = Artifact("Silent Dart") do
+      cost 1
+    end
+
+    class SilentDart < Artifact
+      class ActivatedAbility < ActivatedAbility
+        def costs
+          [
+            Costs::Mana.new(generic: 4),
+            Costs::Sacrifice.new(source)
+          ]
+        end
+
+        def target_choices
+          game.battlefield.creatures
+        end
+
+        def resolve!(target:)
+          trigger_effect(:deal_damage, damage: 3, target: target)
+        end
+      end
+
+      def activated_abilities
+        [ActivatedAbility]
+      end
+    end
+  end
+end

spec/cards/silent_dart_spec.rb

@@ -0,0 +1,20 @@
+require "spec_helper"
+
+RSpec.describe Magic::Cards::SilentDart do
+  include_context "two player game"
+
+  subject(:permanent) { ResolvePermanent("Silent Dart") }
+  let!(:wood_elves) { ResolvePermanent("Wood Elves") }
+
+  it "deals 3 damage to any target" do
+    expect(game.battlefield.creatures.count).to eq(1)
+
+    p1.add_mana(black: 4)
+    p1.activate_ability(ability: permanent.activated_abilities.first) do
+      _1.targeting(wood_elves)
+      _1.pay_mana(generic: { black: 4 })
+    end
+
+    expect(wood_elves.damage).to eq(3)
+  end
+end