How to mock ERP system in JUnit

Question

I'm working on adding JUnit test to an enterprise solution's web services. My question is; how do I - if possible - mock the ERP system in the JUnit tests?

For example I have a getOrders(Connection con, String customerId) method. It, however, makes one call to the ERP system to list all orders like:

public List<Order> getOrders(Connection con, String customerId) {
  // Call ERP system
  orders = con.fetchOrders(customerId);

  // Manipulate result
  orders...

  return orders;      
}

Any way to mock the ERP connection?

Answer 1

I assume you mean mock the Connection object? It's unclear if Connection is an interface or a class. Some mock object libraries only work on interfaces. Here are some of the more popular Java mock object libraries jmock, mockito and easymock

The basic idea would be to create a mock Connection object and have it return data that you want to test.

For example using easymock:

String customerId =...
List<Order> myOrders = ...

Connection mockConnection = EasyMock.createMock(Connection.class);

EasyMock.expect(mockConnection.fetchOrders(customerId)).andReturn(myOrders);
EasyMock.replay(mockConnection);

//call system under test:
List<Orders> results = getOrders(mockConnection, customerId);

List<Orders> expectedResults = ....

assertEquals(expectedResults, results);

Answer 2

If Connection is an interface, then you can simply use something similar to Mockito to verify the messages that are sent to it.

If Connection is a concrete class then it's more difficult. I'd create an interface that duplicated the connection classes public methods and delegated to the appropriate ERP Connection instance.

interface ERPConnection {
   List<Order> fetchOrders(String customerID);
}

class MyConnection implements ERPConnection {
    private Connection _conn;

    public List<Order> fetchOrders(string customerID) {
      return _conn.fetchOrders(customerID);
    }
}

Now in your code you'll rely on the ERPConnection interface rather than the Connection concrete class. This'll feel like a lot of changes, but it'll insulate you from changes to the ERP system and allow you to mock the interface and test the interaction.