adding spec to guard the invoke bundler behavior

Fixes #2731

spec/lib/logstash/bundler_spec.rb

@@ -27,4 +27,94 @@ describe LogStash::Bundler do
       expect(exception.message).to eq("baz")
     end
   end
+  
+  context 'when invoking bundler' do
+    original_stderr = $stderr
+
+    subject { LogStash::Bundler.invoke_bundler!(options) }
+    # by default we want to fail fast on the test
+    let(:options) { { :install => true, :max_tries => 0, :without => [:development]} }
+    let(:bundler_args) { LogStash::Bundler.bundler_arguments(options) }
+
+    before do
+      $stderr = StringIO.new
+
+      expect(::Bundler).to receive(:reset!).at_least(1)
+    end
+
+    after do
+      expect(::Bundler.settings[:path]).to eq(LogStash::Environment::BUNDLE_DIR)
+      expect(::Bundler.settings[:gemfile]).to eq(LogStash::Environment::GEMFILE_PATH)
+      expect(::Bundler.settings[:without]).to eq(options.fetch(:without, []).join(':'))
+
+      expect(ENV['GEM_PATH']).to eq(LogStash::Environment.logstash_gem_home)
+
+      $stderr = original_stderr
+    end
+
+    it 'should call Bundler::CLI.start with the correct arguments' do
+      expect(::Bundler::CLI).to receive(:start).with(bundler_args)
+      subject
+    end
+
+    it 'should abort if a gem is conflicting' do
+      allow(::Bundler::CLI).to receive(:start).with(bundler_args) { raise ::Bundler::VersionConflict.new('conflict') }
+      expect(subject.last).to be_a_kind_of(::Bundler::VersionConflict)
+    end 
+
+    it 'should abort if the gem is not found' do
+      allow(::Bundler::CLI).to receive(:start).with(bundler_args) { raise ::Bundler::GemNotFound.new('conflict') }
+      expect(subject.last).to be_a_kind_of(::Bundler::GemNotFound)
+    end
+
+    it 'should retry until hitting :max_tries on any other error' do 
+      options.merge!({ :max_tries => 2 })
+      expect(::Bundler::CLI).to receive(:start).with(bundler_args).at_most(options[:max_tries] + 1) { raise RuntimeError }
+      subject
+    end
+  end
+
+  context 'when generating bundler arguments' do
+    subject { LogStash::Bundler.bundler_arguments(options) }
+    let(:options) { {} }
+
+    context 'when installing' do
+      let(:options) { { :install => true } }
+    
+      it 'should call bundler install' do
+        expect(subject).to include('install')
+      end
+
+      context 'with the cleaning option' do
+        it 'should add the --clean arguments' do
+          options.merge!(:clean => true)
+          expect(subject).to include('install','--clean')
+        end
+      end
+    end
+
+    context "when updating" do
+      let(:options) { { :update => 'logstash-input-stdin' } }
+
+      context 'with a specific plugin' do
+        it 'should call `bundle update plugin-name`' do
+          expect(subject).to include('update', 'logstash-input-stdin')
+        end
+      end
+
+      context 'with the cleaning option' do
+        it 'should ignore the clean option' do
+          options.merge!(:clean => true)
+          expect(subject).not_to include('--clean')
+        end
+      end
+    end
+
+    context "when only specifying clean" do
+      let(:options) { { :clean => true } }
+      it 'should call the `bundle clean`' do
+        expect(subject).to include('clean')
+      end
+    end
+  end
 end