only run the EM specs if EM is installed

spec/em/em_spec.rb

@@ -1,45 +1,49 @@
 # encoding: UTF-8
-require 'spec_helper'
-require 'mysql2/em'
+if defined? EventMachine
+  require 'spec_helper'
+  require 'mysql2/em'
 
-describe Mysql2::EM::Client do
-  it "should support async queries" do
-    results = []
-    EM.run do
-      client1 = Mysql2::EM::Client.new
-      defer1 = client1.query "SELECT sleep(0.1) as first_query"
-      defer1.callback do |result|
-        results << result.first
-        EM.stop_event_loop
-      end
-
-      client2 = Mysql2::EM::Client.new
-      defer2 = client2.query "SELECT sleep(0.025) second_query"
-      defer2.callback do |result|
-        results << result.first
-      end
-    end
-
-    results[0].keys.should include("second_query")
-    results[1].keys.should include("first_query")
-  end
-
-  it "should support queries in callbacks" do
-    results = []
-    EM.run do
-      client = Mysql2::EM::Client.new
-      defer1 = client.query "SELECT sleep(0.025) as first_query"
-      defer1.callback do |result|
-        results << result.first
-        defer2 = client.query "SELECT sleep(0.025) as second_query"
-        defer2.callback do |result|
+  describe Mysql2::EM::Client do
+    it "should support async queries" do
+      results = []
+      EM.run do
+        client1 = Mysql2::EM::Client.new
+        defer1 = client1.query "SELECT sleep(0.1) as first_query"
+        defer1.callback do |result|
           results << result.first
           EM.stop_event_loop
         end
+
+        client2 = Mysql2::EM::Client.new
+        defer2 = client2.query "SELECT sleep(0.025) second_query"
+        defer2.callback do |result|
+          results << result.first
+        end
       end
+
+      results[0].keys.should include("second_query")
+      results[1].keys.should include("first_query")
     end
 
-    results[0].keys.should include("first_query")
-    results[1].keys.should include("second_query")
+    it "should support queries in callbacks" do
+      results = []
+      EM.run do
+        client = Mysql2::EM::Client.new
+        defer1 = client.query "SELECT sleep(0.025) as first_query"
+        defer1.callback do |result|
+          results << result.first
+          defer2 = client.query "SELECT sleep(0.025) as second_query"
+          defer2.callback do |result|
+            results << result.first
+            EM.stop_event_loop
+          end
+        end
+      end
+
+      results[0].keys.should include("first_query")
+      results[1].keys.should include("second_query")
+    end
   end
+else
+  puts "EventMachine not installed, skipping the specs that use it"
 end