Explore: Add unit tests for addQueryRow() and generateEmptyQuery() (#60977)

* feat: add condition

* refactor: clea up

* refactor: remove changes and add my solution as comment

* feat: add test

* refactor: test preparation

* refactor: finish test prep and remove planned changed from addQueryRow()

* refactor: finish first test

* refactor: add required props after removing any (not complete)

* refactor: replace props and clean up

* refactor: add another test

* refactor: extend tests with datasourceInstance

* refactor: add test for mixed ds enabled

* refactor: remove typescript errors

* feat: add first attempt of a test for generateEmptyQuery()

* feat: setup first test for generateEmptyQuery()

* refactor: remove typescript errors

* feat: add another test for generateEmptyQuery()

* refactor: add some assertions

* refactor: restructure tests

* refactor: remove doubled code

* refactor: remove typescript errors

* refactor: remove mocking mistake and add test

* refactor: remove mocking mistakes

* refactor: repair mock for feature toggle

* refactor: clean up

* refactor: changes from code review

public/app/core/utils/explore.test.ts

@@ -3,6 +3,7 @@ import { serializeStateToUrlParam } from '@grafana/data/src/utils/url';
 import { RefreshPicker } from '@grafana/ui';
 import store from 'app/core/store';
 
+import { DatasourceSrvMock, MockDataSourceApi } from '../../../test/mocks/datasource_srv';
 import { ExploreId } from '../../types';
 
 import {
@@ -19,6 +20,7 @@ import {
   GetExploreUrlArguments,
   getTimeRangeFromUrl,
   getTimeRange,
+  generateEmptyQuery,
 } from './explore';
 
 const DEFAULT_EXPLORE_STATE: ExploreUrlState = {
@@ -27,6 +29,22 @@ const DEFAULT_EXPLORE_STATE: ExploreUrlState = {
   range: DEFAULT_RANGE,
 };
 
+const defaultDs = new MockDataSourceApi('default datasource', { data: ['default data'] });
+
+const datasourceSrv = new DatasourceSrvMock(defaultDs, {
+  'generate empty query': new MockDataSourceApi('generateEmptyQuery'),
+  ds1: {
+    name: 'testDs',
+    type: 'loki',
+  } as MockDataSourceApi,
+});
+
+const getDataSourceSrvMock = jest.fn().mockReturnValue(datasourceSrv);
+jest.mock('@grafana/runtime', () => ({
+  ...(jest.requireActual('@grafana/runtime') as unknown as object),
+  getDataSourceSrv: () => getDataSourceSrvMock(),
+}));
+
 describe('state functions', () => {
   describe('parseUrlState', () => {
     it('returns default state on empty string', () => {
@@ -440,3 +458,28 @@ describe('when buildQueryTransaction', () => {
     expect(transaction.request.interval).toEqual('2h');
   });
 });
+
+describe('generateEmptyQuery', () => {
+  it('should generate query with dataSourceOverride and without queries', async () => {
+    const query = await generateEmptyQuery([], 1, { type: 'loki', uid: 'ds1' });
+
+    expect(query.datasource?.uid).toBe('ds1');
+    expect(query.datasource?.type).toBe('loki');
+    expect(query.refId).toBe('A');
+  });
+  it('should generate query without dataSourceOverride and with queries', async () => {
+    const query = await generateEmptyQuery(
+      [
+        {
+          datasource: { type: 'loki', uid: 'ds1' },
+          refId: 'A',
+        },
+      ],
+      1
+    );
+
+    expect(query.datasource?.uid).toBe('ds1');
+    expect(query.datasource?.type).toBe('loki');
+    expect(query.refId).toBe('B');
+  });
+});