Add test coverage for milestone mutation

spec/frontend/releases/stores/modules/detail/mutations_spec.js

@@ -113,6 +113,26 @@ describe('Release detail mutations', () => {
     });
   });
 
+  describe(`${types.UPDATE_RELEASE_MILESTONES}`, () => {
+    it("updates the release's milestones", () => {
+      state.release = release;
+      const newReleaseMilestones = ['v0.0', 'v0.1'];
+      mutations[types.UPDATE_RELEASE_MILESTONES](state, newReleaseMilestones);
+
+      expect(state.release.milestones).toBe(newReleaseMilestones);
+    });
+  });
+
+  describe(`${types.UPDATE_RELEASE_GROUP_MILESTONES}`, () => {
+    it("updates the release's group milestones", () => {
+      state.release = release;
+      const newReleaseGroupMilestones = ['v0.0', 'v0.1'];
+      mutations[types.UPDATE_RELEASE_GROUP_MILESTONES](state, newReleaseGroupMilestones);
+
+      expect(state.release.groupMilestones).toBe(newReleaseGroupMilestones);
+    });
+  });
+
   describe(`${types.REQUEST_SAVE_RELEASE}`, () => {
     it('set state.isUpdatingRelease to true', () => {
       mutations[types.REQUEST_SAVE_RELEASE](state);