Add pipeline key to Aggregate (#4959)

* Add pipeline key to Aggregate

* clean up

* unit tests

spec/AggregateRouter.spec.js

@@ -0,0 +1,69 @@
+const AggregateRouter = require('../lib/Routers/AggregateRouter').AggregateRouter;
+
+describe('AggregateRouter', () => {
+  it('get pipeline from Array', () => {
+    const body = [{
+      group: { objectId: {} }
+    }];
+    const expected = [ { $group: { _id: {} } } ];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
+
+  it('get pipeline from Object', () => {
+    const body = {
+      group: { objectId: {} }
+    };
+    const expected = [ { $group: { _id: {} } } ];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
+
+  it('get pipeline from Pipeline Operator (Array)', () => {
+    const body = {
+      pipeline: [{
+        group: { objectId: {} }
+      }]
+    };
+    const expected = [ { $group: { _id: {} } } ];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
+
+  it('get pipeline from Pipeline Operator (Object)', () => {
+    const body = {
+      pipeline: {
+        group: { objectId: {} }
+      }
+    };
+    const expected = [ { $group: { _id: {} } } ];
+    const result = AggregateRouter.getPipeline(body);
+    expect(result).toEqual(expected);
+  });
+
+  it('get pipeline fails multiple keys in Array stage ', () => {
+    const body = [{
+      group: { objectId: {} },
+      match: { name: 'Test' },
+    }];
+    try {
+      AggregateRouter.getPipeline(body);
+    } catch (e) {
+      expect(e.message).toBe('Pipeline stages should only have one key found group, match');
+    }
+  });
+
+  it('get pipeline fails multiple keys in Pipeline Operator Array stage ', () => {
+    const body = {
+      pipeline: [{
+        group: { objectId: {} },
+        match: { name: 'Test' },
+      }]
+    };
+    try {
+      AggregateRouter.getPipeline(body);
+    } catch (e) {
+      expect(e.message).toBe('Pipeline stages should only have one key found group, match');
+    }
+  });
+});