health no longer dips below zero

lib/ruby_warrior/units/base.rb

@@ -23,6 +23,8 @@ def take_damage(amount)
         unbind if bound?
         if health
           self.health -= amount
+          # health can't be negative
+          self.health = 0 if self.health < 0
           say "takes #{amount} damage, #{health} health power left"
           if health <= 0
             @position = nil

spec/ruby_warrior/abilities/explode_spec.rb

@@ -10,14 +10,14 @@
     @explode = RubyWarrior::Abilities::Explode.new(@captive)
   end
 
-  it "should subtract 100 health from each unit on the floor" do
+  it "should subtract up to 100 health from each unit on the floor" do
     unit = RubyWarrior::Units::Base.new
     unit.health = 20
     @floor.add(unit, 0, 1)
     @captive.health = 10
     @explode.perform
-    @captive.health.should == -90
-    unit.health.should == -80
+    @captive.health.should == 0
+    unit.health.should == 0
   end
 
   it "should explode when bomb time reaches zero" do
@@ -27,6 +27,6 @@
     @explode.pass_turn
     @captive.health.should == 10
     @explode.pass_turn
-    @captive.health.should == -90
+    @captive.health.should == 0
   end
 end

spec/ruby_warrior/abilities/throw_spec.rb

@@ -40,7 +40,7 @@
     captive.add_abilities :explode!
     @floor.add(captive, 1, 1)
     @detonate.perform
-    captive.health.should == -99
-    @warrior.health.should == -80
+    captive.health.should == 0
+    @warrior.health.should == 0
   end
 end