Add test for cron concurrency policy

tests/unit/cron.bats

@@ -235,6 +235,30 @@ teardown() {
   assert_output "['task.py', 'schedule', 'now']"
 }
 
+@test "(cron) cron:run concurrency_policy forbid" {
+  run deploy_app dockerfile dokku@$DOKKU_DOMAIN:$TEST_APP template_cron_file_concurrency_forbid
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  
+  cron_id="$(dokku cron:list $TEST_APP --format json | jq -r '.[0].id')"
+  run /bin/bash -c "echo cron $cron_id"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output_exists
+
+  run /bin/bash -c "dokku cron:run $TEST_APP $cron_id --detach"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku cron:run $TEST_APP $cron_id"
+  echo "output: $output"
+  echo "status: $status"
+  assert_failure
+}
+
 @test "(cron) cron:suspend cron:resume" {
   run deploy_app python dokku@$DOKKU_DOMAIN:$TEST_APP template_cron_file_valid_multiple
   echo "output: $output"
@@ -427,3 +451,21 @@ template_cron_file_valid_multiple() {
 }
 EOF
 }
+
+template_cron_file_concurrency_forbid() {
+  local APP="$1"
+  local APP_REPO_DIR="$2"
+  [[ -z "$APP" ]] && local APP="$TEST_APP"
+  echo "injecting valid cron app.json -> $APP_REPO_DIR/app.json"
+  cat <<EOF >"$APP_REPO_DIR/app.json"
+{
+  "cron": [
+    {
+      "command": "sleep 5",
+      "schedule": "0 0 * * *",
+      "concurrency_policy": "forbid"
+    }
+  ]
+}
+EOF
+}