Bank integrations display

A simple bank aggregation application that pulls information from multiple different banks and displays it. The challenge here is that we don’t want the BankController to ever directly use any classes in the com.bank1 and com.bank2 packages

Design

In order to isolates BankController from bank1 and bank2 implementation details, this class depends only to an standard interface IBankIntegrationService. This interface defines the necessary methods to bring all information needed from all banks integrations, transformed in the domain data structure.

To do this, I took advantage of the Dependency Injection design pattern to avoid the high level of code coupling between my controller and the services. Thus, the controller depends on an interface and not directly an specific implementation. As you can see in the diagram below:

In this way, the services that communicates with Bank1 and Bank2 need to implement the interface for a BankIntegrationService. Since they both expose functionality to fetch account balances and transactions, I used the Adapter pattern to build the services that implement the standard interface defined in the application.

I also noticed that the way the transactions are returned are the same between the banks, as well as the implementation necessary to map them in Transactions of the client application's domain. So, I decided that having an abstract BankIntegrationService class could help with reusability. In this way, each BankAdapter only needs to worry about implementing what is specific to its own domain, leaving the class they inherit from.

At last, the BankAdapters also take advantage of Dependency Injection: by transferring the responsibility of instantiating the specific classes of BankAccountSource to whoever instantiates the Adapters.

Setup & Run

This Node.js project uses typescript, which will be automatically installed as a development dependency. However, make sure your environment has the following at least:

• node.js
• npm

Install all project dependencies

npm install

This application uses environment variables as required inputs. In order to run it, you need to create an file named .env and put all variables required (see the .env.example file):

ACCOUNT_NUMBER=
FETCH_TRANSACTIONS_FROM_DATE=
FETCH_TRANSACTIONS_TO_DATE=

Then, execute the application to print all balances and transactions from current Bank Integrations

npm start

Test

I took advantage of the project to test a new test library that I had never used: Vitest, as an alternative to the well-known Jest.

*Why vitest?

To test typescript files, we need to transpile them during testing. Vitest do that natively, so we don't need to deal with the complexity of transforming source files. Watch mode is enabled by default, aligning itself with the way Vite pushes for a dev first experience. Also, Vitest cares a lot about performance and uses Worker threads to run as much as possible in parallel.

I found it interesting and it turned out to be really useful and fast.

Execute the following command to run all test suites and log mocked results:

npm test

In order to see a test coverage report, run:

 npm run test:coverage

Then, you should see the results like this: