Stubbed the calls to set the logger on Delayed::Worker module.

The class variable was leaking into other tests.

spec/delayed/command_spec.rb

@@ -12,7 +12,8 @@
     allow(Dir).to receive(:chdir)
     allow(Logger).to receive(:new).and_return(logger)
     allow_any_instance_of(Delayed::Worker).to receive(:start)
-    Delayed::Worker.logger = nil
+    allow(Delayed::Worker).to receive(:logger=)
+    allow(Delayed::Worker).to receive(:logger).and_return(nil, logger)
   end
 
   shared_examples_for 'uses --log-dir option' do
@@ -28,8 +29,8 @@
 
   describe 'run' do
     it 'sets the Delayed::Worker logger' do
+      expect(Delayed::Worker).to receive(:logger=).with(logger)
       subject.run
-      expect(Delayed::Worker.logger).to be logger
     end
 
     context 'when Rails root is defined' do
@@ -67,11 +68,6 @@
         subject.run
       end
 
-      it 'sets the Delayed::Worker logger' do
-        subject.run
-        expect(Delayed::Worker.logger).to be logger
-      end
-
       context 'when --log-dir is not specified' do
         it 'creates the delayed_job.log in $PWD/log' do
           expect(Logger).to receive(:new).with("#{Delayed::Command::DIR_PWD}/log/delayed_job.log")