What is this repository for?

Test task for Revolut Backend Test Engineer

Tech stack used behind this test project :

• Dropwizard as web service framework.
• Apache Hibernate for ORM.
• H2 in memory database.
• Apache Maven as build tool.
• JUnit as a test framework
• Mockito for mocking.
• JaCoCo for code coverage library.

Requirements:

Things you need to have installed to run the test project.

• Git
• Apache Maven
• JDK

Running the application:

• Clone the project.

  git clone https://github.com/shihabcsedu09/revolut-money-transfer
  

• Go to the project.

  cd revolut-money-transfer
  

• Run this command

  bash scripts/run.sh
  

• Alternatively you can run the following commands too

  mvn clean package  
  java -jar target/money-transfer-1.0-SNAPSHOT.jar server config.yml
  

• The application is deployed at http://localhost:8080/

• You can find the test coverage report at target/site/jacoco/index.html

How the application handles transaction and concurrent transfer

1. @UnitOfWork annotation over jersey resource method make sure the transaction atomicity.
2. Optimistic Lock is implemented by adding a version attribute in the entity class. That ensures if other transaction updates the account entity in the middle of a transfer it will no commit the current one by checking the version number.

Available APIs

Account API:

POST: Before transfering amount you need to first create a source acccount and a destination account with balance. This you can do by send a post request /account endpoint with the following as a request body.

{
  "name" : "Some Test Account",
  "balance" : 100.22
}

Parameter	Type	Description
name	string	Required. The name of the account
balance	decimal	Required. The initial balance of the amount, must be a positive decimal

Corresponding cURL command:

curl -X POST \
  http://localhost:8080/account/ \
  -H 'content-type: application/json' \
  -d '{
  "name" : "Some Test Account",
  "balance" : 100.22
}'

As a response you will get the following

{
    "id": 1,
    "name": "Some Test Account",
    "balance": 100.22
}

Keep track of this id as it is needed to transfer money from one account to another.

Available status code for this API endpoint :

Status Code	Description	Comment
200	OK	If the applications successfully creates the account
400	Bad Request	If the json is malformed
422	UNPROCESSABLE ENTITY	If parameter constraints violates like giving negative balance
500	INTERNAL SERVER ERROR	If something bad happened in the server

GET: You can fetch account informaton by sending a GET request with account id as a path parameter to the following endpoint. /account/{accountId}

Example request:

curl -X GET \
  http://localhost:8080/account/1 \
  -H 'content-type: application/json' \

As a response you will get the following

{
    "id": 1,
    "name": "Some Test Account",
    "balance": 100.22
}

Available status code for this API endpoint :

Status Code	Description	Comment
200	OK	If the applications successfully fetches the account
600	NO ACCOUNT FOUND	If no account found for this id
500	INTERNAL SERVER ERROR	If something bad happened in the server

Transfer API:

POST: To make a transfer we need to define the source account, destination account and transfer amount first. Then a post request with this information to /transfer endpoint will make the transfer.

{
	"fromAccountId": 2,
	"toAccountId": 1,
	"amount": 100
}

Parameter	Type	Description
fromAccountId	long	Required. The id of the source account
toAccountId	long	Required. The id of the destination account
amount	decimal	Required. The transfer amount, must be a positive decimal

Corresponding cURL command:

curl -X POST \
  http://localhost:8080/transfer/ \
  -H 'content-type: application/json' \
  -d '{
	"fromAccountId": 2,
	"toAccountId": 1,
	"amount": 100
}'

As a response you will get the following

{
	"fromAccountId": 2,
	"toAccountId": 1,
	"amount": 100
}

Available status code for this API endpoint :

Status Code	Description	Comment
200	OK	If the applications successfully transfer the amount
400	Bad Request	If the json is malformed
422	UNPROCESSABLE ENTITY	If parameter constraints violates like giving negative balance
601	SOURCE ACCOUNT NOT FOUND	If non exisiting source account id given
602	DESTINATION ACCOUNT NOTFOUND	If non exisiting destination account id given
603	NOT ENOUGH BALANCE	If the source account don't have enough balance
604	ACCOUNT ALREADY UPDATED	If the account is already updated by another transaction concurrently
500	INTERNAL SERVER ERROR	If something bad happened in the server

Limitations

1. Load/Stress test of the application to see how it works with concurrent requests
2. Swagger integration for api documentation
3. Code Quality linters integration like sonar cloud.
4. More granular exception mapping.