fix onLicenseInfoChange callback to be called on update (elastic#53559)

x-pack/legacy/plugins/xpack_main/server/lib/__tests__/xpack_info.js

@@ -312,6 +312,54 @@ describe('XPackInfo', () => {
     });
   });
 
+  it('onLicenseInfoChange() allows to subscribe to license update', async () => {
+    const license$ = new BehaviorSubject(createLicense());
+
+    const xPackInfo = new XPackInfo(mockServer, {
+      licensing: {
+        license$,
+        refresh: () => null,
+      },
+    });
+
+    const watcherFeature = xPackInfo.feature('watcher');
+    watcherFeature.registerLicenseCheckResultsGenerator(info => ({
+      type: info.license.getType(),
+    }));
+
+    const statuses = [];
+    xPackInfo.onLicenseInfoChange(() => statuses.push(watcherFeature.getLicenseCheckResults()));
+
+    license$.next(createLicense({ type: 'basic' }));
+    expect(statuses).to.eql([{ type: 'basic' }]);
+
+    license$.next(createLicense({ type: 'trial' }));
+    expect(statuses).to.eql([{ type: 'basic' }, { type: 'trial' }]);
+  });
+
+  it('refreshNow() leads to onLicenseInfoChange()', async () => {
+    const license$ = new BehaviorSubject(createLicense());
+
+    const xPackInfo = new XPackInfo(mockServer, {
+      licensing: {
+        license$,
+        refresh: () => license$.next({ type: 'basic' }),
+      },
+    });
+
+    const watcherFeature = xPackInfo.feature('watcher');
+
+    watcherFeature.registerLicenseCheckResultsGenerator(info => ({
+      type: info.license.getType(),
+    }));
+
+    const statuses = [];
+    xPackInfo.onLicenseInfoChange(() => statuses.push(watcherFeature.getLicenseCheckResults()));
+
+    await xPackInfo.refreshNow();
+    expect(statuses).to.eql([{ type: 'basic' }]);
+  });
+
   it('getSignature() returns correct signature.', async () => {
     const license$ = new BehaviorSubject(createLicense());
     const xPackInfo = new XPackInfo(mockServer, {

x-pack/legacy/plugins/xpack_main/server/lib/xpack_info.ts

@@ -101,6 +101,8 @@ export class XPackInfo {
           error: license.error,
         };
       }
+
+      this._licenseInfoChangedListeners.forEach(fn => fn());
     });
 
     this._license = new XPackInfoLicense(() => this._cache.license);