Author: Rob Rico

Testing many functions or class methods together is known as Integration Testing. The integration test should be relatively small in scope and cover only a handful of functions.

A simple example

Taking our fruity example we can build an integration test to ensure the Fruit, and the Order classes work together in tandem. Let’s see how the two are defined:

// Fruit.*
class Fruit {
    name: string;
    price: number;
    getPrice() {
        return this.price;
    }
}

// Order.*
class Order {
    details: string;
    getTotal(fruit: Fruit, qty: number) {
        return fruit.getPrice() * qty;
    }
    setDetails(details: string) {
        this.details = details;
    }
    getDetails() {
        return details;
    }
}

When we Unit Tested Order our TDD strategy was to test the individual function getTotal. Let’s test that same function, but in an integration test.

test("Test Fruit & Order Integration", () => {
    const fruit = new Fruit(10)
    const order = new Order();
    const orderTotal = order.getTotal(fruit,20);

    // Assert total to return proper price
    expect(orderTotal).toBe(200);
});

It may seem kind of strange to test the getTotal function again in an integration test, but this test allows us to assert the following.
1) The function orderTotal is returning the correct total using a non-mock Fruit object
2) The Fruit object is correctly returning it’s price in the context of this integration
3) Order is correctly calculating the total using a non-mock Fruit object