Fix RUBY-1752 Stubbing out Time.now in tests can cause tests to break (#1289)

Author: p-mongo

lib/mongo/server/description.rb

@@ -196,7 +196,7 @@ def initialize(address, config = {}, average_round_trip_time = nil)
           @features = Features.new(wire_versions, me || @address.to_s)
         end
         @average_round_trip_time = average_round_trip_time
-        @last_update_time = Time.now.freeze
+        @last_update_time = Time.now.dup.freeze
 
         if Mongo::Lint.enabled?
           # prepopulate cache instance variables

spec/mongo/server/description_spec.rb

@@ -49,6 +49,20 @@
     end
   end
 
+  describe '#initialize' do
+    context 'when Time.now is mocked' do
+      it 'does not freeze mocked time' do
+        obj = Time.now
+        expect(Time).to receive(:now).at_least(:once).and_return(obj)
+        expect(obj.frozen?).to be false
+
+        description = described_class.new(address)
+        expect(description.last_update_time).to eq(obj)
+        expect(obj.frozen?).to be false
+      end
+    end
+  end
+
   describe '#arbiters' do
 
     context 'when the replica set has arbiters' do