prometheus nested query support

public/app/plugins/datasource/prometheus/specs/datasource_specs.ts

@@ -590,4 +590,19 @@ describe('PrometheusDatasource', function() {
       expect(query.scopedVars.__interval_ms.value).to.be(5 * 1000);
     });
   });
+  describe('The nested query', function() {
+    it('should generate correct query', function() {
+      let query = 'sum(rate(#A[1m]))';
+      let options = {
+        targets: [
+          {
+            refId: 'A',
+            expr: 'http_requests_total'
+          }
+        ]
+      };
+      let result = ctx.ds.replaceNestedQuery(query, options);
+      expect(result).to.be('sum(rate(http_requests_total[1m]))');
+    });
+  });
 });