add query test fot /cohorts/:cohortId route to be sure the delete done

relates #29

test/index.test.js

@@ -13,14 +13,18 @@ afterAll(() => {
 });
 
 describe('Admin, (/cohorts/:cohortId)', () => {
-  test('Route /cohorts/1 status 200, json header, data.message = Cohort deleted successfully ', (done) => {
+  test('Route /cohorts/1 status 200, data.message = Cohort deleted successfully ', (done) => {
     return request(app)
       .delete('/api/v1/cohorts/1')
       .expect(200)
       .expect('Content-Type', /json/)
-      .end((err, res) => {
+      .end(async (err, res) => {
         const { data } = res.body;
         if (err) return done(err);
+        const result = await connection.query(
+          'SELECT * from cohort WHERE id = 1',
+        );
+        expect(result.rows).toHaveLength(0);
         expect(data.message).toBe('Cohort deleted successfully');
         done();
       });