Reject serialized execution without a task (#1113)

* Reject serialized execution without a task

* Add serialized execution block coverage

---------

Co-authored-by: Songstats Dependency Audit <audit@local.invalid>

Author: OskarEichler

lib/concurrent-ruby/concurrent/executor/serialized_execution.rb

@@ -32,6 +32,8 @@ def call
     #
     # @raise [ArgumentError] if no task is given
     def post(executor, *args, &task)
+      raise ArgumentError.new('no block given') unless block_given?
+
       posts [[executor, args, task]]
       true
     end

spec/concurrent/executor/serialized_execution_spec.rb

@@ -4,6 +4,15 @@
 
 module Concurrent
 
+  RSpec.describe SerializedExecution do
+
+    it 'raises an exception when no block is given' do
+      expect {
+        subject.post(ImmediateExecutor.new)
+      }.to raise_error(ArgumentError, 'no block given')
+    end
+  end
+
   RSpec.describe SerializedExecutionDelegator do
 
     subject { SerializedExecutionDelegator.new(ImmediateExecutor.new) }