Fix broken TopN test (#72)

We had previously assumed that mget calls would always happen. However,
if there was no data from the initial search calls, then mget would not
be called, thus, the assertion failed.

Since we are making calls that return no data, I changed the assertion.
I also checked if response was valid (expected status code, expected
data type in the payload).

src/plugins/profiling/server/routes/topn.test.ts

@@ -35,8 +35,8 @@ describe('TopN data from Elasticsearch', () => {
   });
 
   describe('when fetching Stack Traces', () => {
-    it('should search first then mget', async () => {
-      await topNElasticSearchQuery(
+    it('should search first then skip mget', async () => {
+      const response = await topNElasticSearchQuery(
         client,
         logger,
         index,
@@ -47,8 +47,14 @@ describe('TopN data from Elasticsearch', () => {
         'StackTraceID',
         kibanaResponseFactory
       );
+
+      // Calls to mget are skipped since data doesn't exist
       expect(client.search).toHaveBeenCalledTimes(2);
-      expect(client.mget).toHaveBeenCalledTimes(2);
+      expect(client.mget).toHaveBeenCalledTimes(0);
+
+      expect(response.status).toEqual(200);
+      expect(response.payload).toHaveProperty('TopN');
+      expect(response.payload).toHaveProperty('Metadata');
     });
   });
 });