(POOLER-73) Add spec tests for check_snapshot_queue

Add spec tests for check_snapshot_queue

Previously the check_snapshot_queue method would execute the loop indefinitely
as it did not have a terminating condition.  This made it impossible to test.
This commit modifies the check_snapshot_queue method so that it can take a
maxloop and delay parameter so that it can be tested.

lib/vmpooler/pool_manager.rb

@@ -443,15 +443,21 @@ module Vmpooler
       end
     end
 
-    def check_snapshot_queue
+    def check_snapshot_queue(maxloop = 0, loop_delay = 5)
       $logger.log('d', "[*] [snapshot_manager] starting worker thread")
 
       $vsphere['snapshot_manager'] ||= Vmpooler::VsphereHelper.new $config, $metrics
 
       $threads['snapshot_manager'] = Thread.new do
+        loop_count = 1
         loop do
           _check_snapshot_queue $vsphere['snapshot_manager']
-          sleep(5)
+          sleep(loop_delay)
+
+          unless maxloop.zero?
+            break if loop_count >= maxloop
+            loop_count = loop_count + 1
+          end
         end
       end
     end

spec/unit/pool_manager_spec.rb

@@ -1021,6 +1021,72 @@ EOT
     end
   end
 
+  describe '#check_snapshot_queue' do
+    let(:threads) {[]}
+
+    before(:each) do
+      expect(Thread).to receive(:new).and_yield
+      allow(subject).to receive(:_check_snapshot_queue)
+    end
+
+    it 'should log the disk manager is starting' do
+      expect(logger).to receive(:log).with('d', "[*] [snapshot_manager] starting worker thread")
+
+      expect($threads.count).to be(0)
+      subject.check_snapshot_queue(1,0)
+      expect($threads.count).to be(1)
+    end
+
+    it 'should add the manager to the global thread list' do
+      # Note - Ruby core types are not necessarily thread safe
+      expect($threads.count).to be(0)
+      subject.check_snapshot_queue(1,0)
+      expect($threads.count).to be(1)
+    end
+
+    it 'should call _check_snapshot_queue' do
+      expect(subject).to receive(:_check_snapshot_queue).with(Vmpooler::VsphereHelper)
+
+      subject.check_snapshot_queue(1,0)
+    end
+
+    context 'delays between loops' do
+      let(:maxloop) { 2 }
+      let(:loop_delay) { 1 }
+      # Note a maxloop of zero can not be tested as it never terminates
+
+      it 'defaults to 5 second loop delay' do
+        expect(subject).to receive(:sleep).with(5).exactly(maxloop).times
+        subject.check_snapshot_queue(maxloop)
+      end
+
+      it 'when a non-default loop delay is specified' do
+        start_time = Time.now
+        subject.check_snapshot_queue(maxloop,loop_delay)
+        finish_time = Time.now
+
+        # Use a generous delta to take into account various CPU load etc.
+        expect(finish_time - start_time).to be_within(0.75).of(maxloop * loop_delay)
+      end
+    end
+
+    context 'loops specified number of times (5)' do
+      let(:maxloop) { 5 }
+      # Note a maxloop of zero can not be tested as it never terminates
+
+      after(:each) do
+        # Reset the global variable - Note this is a code smell
+        $threads = nil
+      end
+
+      it 'should call _check_snapshot_queue 5 times' do
+        expect(subject).to receive(:_check_snapshot_queue).with(Vmpooler::VsphereHelper).exactly(maxloop).times
+
+        subject.check_snapshot_queue(maxloop,0)
+      end
+    end
+  end
+
   describe '#migration_limit' do
     # This is a little confusing.  Is this supposed to return a boolean
     # or integer type?