Add issauble_context_spec

spec/javascripts/issuable_context_spec.js

+import '~/issuable_context';
+
+fdescribe('IssuableContext', () => {
+  describe('toggleHiddenParticipants', () => {
+    beforeEach(() => {
+
+    });
+
+    fit('calls loadCheck if lazyLoader is set', () => {
+      gl.lazyLoader = jasmine.createSpyObj('lazyLoader', ['loadCheck']);
+      const event = {};
+
+      IssuableContext.prototype.toggleHiddenParticipants(event);
+
+      expect(gl.lazyLoader.loadCheck).toHaveBeenCalled();
+    });
+
+    it('does not call loadCheck if lazyLoader is not set', () => {
+      gl.lazyLoader = undefined;
+      const event = {};
+
+      IssuableContext.prototype.toggleHiddenParticipants(event);
+
+      expect(gl.lazyLoader.loadCheck).not.toHaveBeenCalled();
+    });
+
+    afterEach(() => {
+      gl.lazyLoader = undefined;
+    });
+  });
+});