(#170) Add ability to remove gem from appraisal

lib/appraisal/bundler_dsl.rb

@@ -25,7 +25,11 @@ def run(&block)
     end
 
     def gem(name, *requirements)
-      @dependencies.add(name, substitute_git_source(requirements))
+      if requirements.include?(:remove)
+        @dependencies.remove(name)
+      else
+        @dependencies.add(name, substitute_git_source(requirements))
+      end
     end
 
     def group(*names, &block)

lib/appraisal/dependency_list.rb

@@ -4,10 +4,19 @@ module Appraisal
   class DependencyList
     def initialize
       @dependencies = Hash.new
+      @removed_dependencies = Set.new
     end
 
     def add(name, requirements)
-      @dependencies[name] = Dependency.new(name, requirements)
+      unless @removed_dependencies.include?(name)
+        @dependencies[name] = Dependency.new(name, requirements)
+      end
+    end
+
+    def remove(name)
+      if @removed_dependencies.add?(name)
+        @dependencies.delete(name)
+      end
     end
 
     def to_s

spec/acceptance/appraisals_file_bundler_dsl_compatibility_spec.rb

@@ -2,7 +2,8 @@
 
 describe 'Appraisals file Bundler DSL compatibility' do
   it 'supports all Bundler DSL in Appraisals file' do
-    build_gems %w(bagel orange_juice milk waffle coffee ham sausage pancake)
+    build_gems %w(bagel orange_juice milk waffle coffee ham
+                  sausage pancake rotten_egg)
     build_git_gems %w(egg croissant pain_au_chocolat omelette)
 
     build_gemfile <<-Gemfile
@@ -24,6 +25,7 @@
       group :breakfast do
         gem 'orange_juice'
         gem "omelette", :custom_git_source => "omelette"
+        gem 'rotten_egg'
       end
 
       platforms :ruby, :jruby do
@@ -58,6 +60,7 @@
         end
 
         group :breakfast do
+          gem 'rotten_egg', :remove
           gem 'bacon'
 
           platforms :rbx do

spec/appraisal/dependency_list_spec.rb

@@ -28,4 +28,23 @@
       expect(dependency_list.to_s).to eq %(gem "rails", "4.1.4")
     end
   end
+
+  describe "#remove" do
+    let(:dependency_list) { Appraisal::DependencyList.new }
+
+    before do
+      dependency_list.add("rails", ["4.1.4"])
+    end
+
+    it "removes the dependency from the list" do
+      dependency_list.remove("rails")
+      expect(dependency_list.to_s).to eq("")
+    end
+
+    it "respects the removal over an addition" do
+      dependency_list.remove("rails")
+      dependency_list.add("rails", ["4.1.0"])
+      expect(dependency_list.to_s).to eq("")
+    end
+  end
 end