Re-implement the event generator as a new-style plugin - Mct4552 (#4620)

Updates Event Generator to ES6 classes and current API.

Co-authored-by: Andrew Henry <akhenry@gmail.com>
Co-authored-by: John Hill <john.c.hill@nasa.gov>

example/eventGenerator/pluginSpec.js

@@ -0,0 +1,69 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2022, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+import EventMessageGeneratorPlugin from './plugin.js';
+import {
+    createOpenMct,
+    resetApplicationState
+} from '../../src/utils/testing';
+
+describe('the plugin', () => {
+    let openmct;
+    const mockDomainObject = {
+        identifier: {
+            namespace: '',
+            key: 'some-value'
+        },
+        telemetry: {
+            duration: 0
+        },
+        type: 'eventGenerator'
+    };
+
+    beforeEach((done) => {
+        const options = {};
+        openmct = createOpenMct();
+        openmct.install(new EventMessageGeneratorPlugin(options));
+        openmct.on('start', done);
+        openmct.startHeadless();
+    });
+
+    afterEach(async () => {
+        await resetApplicationState(openmct);
+    });
+
+    describe('the plugin', () => {
+        it("supports subscription", (done) => {
+            const unsubscribe = openmct.telemetry.subscribe(mockDomainObject, (telemetry) => {
+                expect(telemetry).not.toEqual(null);
+                expect(telemetry.message).toContain('CC: Eagle, Houston');
+                expect(unsubscribe).not.toEqual(null);
+                unsubscribe();
+                done();
+            });
+        });
+
+        it("supports requests", async () => {
+            const telemetry = await openmct.telemetry.request(mockDomainObject);
+            expect(telemetry[0].message).toContain('CC: Eagle, Houston');
+        });
+    });
+});