Skip verification of Docker image if pool size is empty

app/models/execution_environment.rb

@@ -78,7 +78,8 @@ class ExecutionEnvironment < ApplicationRecord
   end
 
   def validate_docker_image?
-    docker_image.present? && !Rails.env.test?
+    # We only validate the code execution with the provided image if there is at least one container to test with.
+    pool_size.positive? && docker_image.present? && !Rails.env.test?
   end
 
   def working_docker_image?

spec/controllers/execution_environments_controller_spec.rb

@@ -13,7 +13,7 @@ describe ExecutionEnvironmentsController do
 
   describe 'POST #create' do
     context 'with a valid execution environment' do
-      let(:perform_request) { proc { post :create, params: {execution_environment: FactoryBot.build(:ruby).attributes} } }
+      let(:perform_request) { proc { post :create, params: {execution_environment: FactoryBot.build(:ruby, pool_size: 1).attributes} } }
 
       before do
         allow(Rails.env).to receive(:test?).and_return(false, true)
@@ -186,7 +186,7 @@ describe ExecutionEnvironmentsController do
         runner = instance_double 'runner'
         allow(Runner).to receive(:for).and_return(runner)
         allow(runner).to receive(:execute_command).and_return({})
-        put :update, params: {execution_environment: FactoryBot.attributes_for(:ruby), id: execution_environment.id}
+        put :update, params: {execution_environment: FactoryBot.attributes_for(:ruby, pool_size: 1), id: execution_environment.id}
       end
 
       expect_assigns(docker_images: Array)

spec/models/execution_environment_spec.rb

@@ -138,8 +138,14 @@ describe ExecutionEnvironment do
       expect(execution_environment.send(:validate_docker_image?)).to be false
     end
 
+    it 'is false when the pool size is empty' do
+      expect(execution_environment.pool_size).to be 0
+      expect(execution_environment.send(:validate_docker_image?)).to be false
+    end
+
     it 'is true otherwise' do
       execution_environment.docker_image = FactoryBot.attributes_for(:ruby)[:docker_image]
+      execution_environment.pool_size = 1
       allow(Rails.env).to receive(:test?).and_return(false)
       expect(execution_environment.send(:validate_docker_image?)).to be true
     end