Mocha MongoDB clean collection before each test - mongodb

Question

I'm trying to cleanup 2 collections before each test. I'm using mocha --watch to rerun tests while editing the test source files. First run always executes as expected, but consecutive runs gives Topology was destroyed error from mongodb(indicated via result of http request).
I am not really sure why deleteMany deletes my inserted object in consecutive runs.
describe('myCollection1 related tests', () => {
// myCollection1 documents should refer to a valid myCollection2 document.
var foo;
const exampleObject = {name: 'TEST OBJECT', attr1: 'TO'};
beforeEach(() => {
return Promise.all([
mongo.db('mydb').collection('myCollection1').deleteMany({}), // clear collection 1
mongo.db('mydb').collection('myCollection2').deleteMany({}) // clear collection 2
.then(() => mongo.db('mydb').collection('myCollection2').insertOne(exampleObject) // and add a sample object
.then((value) => {
foo = value.ops[0]; // save this as test specific variable so I can use it in my tests.
return Promise.resolve();
})),
]);
});
it('should create a related object', (done) => {
chai.request(server)
.post('/api/v1/foos/')
.send({ related: foo._id })
.then((res) => {
res.should.have.status(200);
res.body.should.be.an('object').with.all.keys('status', 'errors', 'data');
done();
}).catch((err) => {
done(err);
});
});
});

Answer 1

I spotted issue with your promise structure in beforeEach. I'm not sure it is intended or not. I'm afraid it is the culprit. I'm fixing that into below:
beforeEach(() => {
return Promise.all([
mongo.db('mydb').collection('myCollection1').deleteMany({}),
mongo.db('mydb').collection('myCollection2').deleteMany({})
]) // close the promise.all here
.then(() => collections.engines().insertOne(exampleObject)) // close `then` here
.then((value) => {
foo = value.ops[0];
return Promise.resolve();
});
});
Hope it helps