feat: add Subscription base class on app instance

lib/egg.js

@@ -142,6 +142,13 @@ class EggApplication extends EggCore {
      * @since 1.0.0
      */
     this.Service = BaseContextClass;
+
+    /**
+     * Retreive base subscription
+     * @member {Subscription} Subscription
+     * @since 2.12.0
+     */
+    this.Subscription = BaseContextClass;
   }
 
   /**

test/fixtures/apps/schedule/app/schedule/hello.js

@@ -0,0 +1,17 @@
+'use strict';
+
+module.exports = app => {
+  return class LoggerExample extends app.Subscription {
+    static get schedule() {
+      return {
+        type: 'worker',
+        cron: '0 0 3 * * *',
+        immediate: true,
+      };
+    }
+
+    async subscribe() {
+      this.ctx.logger.info('Info about your task');
+    }
+  }
+};

test/fixtures/apps/schedule/app/schedule/sub/cron.js

@@ -6,5 +6,5 @@ exports.schedule = {
 };
 
 exports.task = function* (ctx) {
-  ctx.logger.warn('cron');
+  ctx.logger.warn('cron wow');
 };

test/lib/plugins/schedule.test.js

@@ -17,9 +17,12 @@ describe('test/lib/plugins/schedule.test.js', () => {
     await sleep(7000);
     await app.close();
     const log = getLogContent('schedule');
-    const count = contains(log, 'cron');
+    const count = contains(log, 'cron wow');
     assert(count >= 1);
     assert(count <= 2);
+
+    // should support Subscription class on app.Subscription
+    assert(contains(log, 'Info about your task') === 1);
   });
 });