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Basics of Mocking

Mocking is a process used in unit testing when the unit being tested has external dependencies. The purpose of mocking is to isolate and focus on the code being tested and not on the behavior or state of external dependencies. In mocking, the dependencies are replaced by closely controlled replacement objects that simulate the behavior of the real ones. JustMock creates the replacement objects and manages their lifetime for you.

In the topics of this Getting Started section, you will get familiar with the API of JustMock and will see example scenarios of its basic usage.

Mock the Behavior of a Public Method

To start from the basics, in the first example we will show you how to mock the behavior of a public method for a specific instance. To demonstrate the case, we will use a sample setup representing an order and a warehouse keeping all the inventory for the different orders:

Sample setup

public class Warehouse 
{ 
    public Dictionary<string, int> Products { get; set; } 
 
    public bool HasInventory(string productName, int quantity) 
    { 
        int quantityInWarehouse; 
        if (this.Products.TryGetValue(productName, out quantityInWarehouse)) 
        { 
            if (quantityInWarehouse >= quantity) 
            { 
                return true; 
            } 
        } 
 
        return false; 
    } 
 
    public void Remove(string productName, int quantity) 
    { 
        if (this.HasInventory(productName, quantity)) 
        { 
            this.Products[productName] -= quantity; 
        } 
    } 
} 
 
public class Order 
{ 
    public Order(string productName, int quantity) 
    { 
        this.ProductName = productName; 
        this.Quantity = quantity; 
    } 
 
    public string ProductName { get; private set; } 
    public int Quantity { get; private set; } 
    public bool IsCompleted { get; private set; } 
 
    public void Complete(Warehouse warehouse) 
    { 
        if (warehouse.HasInventory(this.ProductName, this.Quantity)) 
        { 
            warehouse.Remove(this.ProductName, this.Quantity); 
            this.IsCompleted = true; 
        } 
    } 
} 

Let’s first verify that the Complete method of the Order class properly sets the IsCompleted property to avoid duplication. Our target method depends on the products currently present in the Products collection and internally invokes other two methods - HasInventory and Remove. To test the code without mocking, you would need to setup a Warehouse object with a collection keeping the products and maintain that collection during the execution of the different tests. You would have to call the Complete method using specific arguments for the different cases.

With JustMock, you can directly control the behavior of the methods and ignore the specific data preserved in Warehouse. Example 1 shows how you can setup the HasInventory method to always return true and ignore the logic of Remove. The demonstrated setup enables you to focus on the logic and ignore the specific data or requirements for the logic to operate.

Example 1: Test IsCompleted marked as expected by controlling the method behavior

[TestMethod] 
public void Order_IsCompleted_WhenWarehouseHasInventory() 
{ 
    Order order = new Order("testProduct", 10); 
    Warehouse warehouse = new Warehouse(); 
 
    // Setup the warehouse - the HasInventory method called with the specified parameters will always return true.  
    Mock.Arrange(() => warehouse.HasInventory(order.ProductName, order.Quantity)).Returns(true); 
 
    // We are not maintaining a collection of products, so there isn't anything to remove.  
    Mock.Arrange(() => warehouse.Remove(order.ProductName, order.Quantity)).DoNothing(); 
 
    order.Complete(warehouse); 
 
    Assert.IsTrue(order.IsCompleted); 
} 

Another option that you can use is to create a collection of products and ensure the Products property uses it instead of messing up the real data.

Example 2: Test IsCompleted marked as expected by controlling the Products property behavior

private Dictionary<string, int> GetTestProducts() 
{ 
    return new Dictionary<string, int>() 
    { 
        { "shirt", 23}, 
        { "trousers", 3}, 
        { "hat", 12}, 
        { "jeans", 36}, 
        { "skirt", 9} 
    }; 
} 
 
[TestMethod] 
public void Order_IsCompleted_WhenWarehouseHasSampleInventory() 
{ 
    Order order = new Order("shirt", 1); 
    Warehouse warehouse = new Warehouse(); 
 
    // Setup the warehouse - the Products property will always return the test products.  
    Mock.Arrange(() => warehouse.Products).Returns(this.GetTestProducts()); 
 
    order.Complete(warehouse); 
 
    Assert.IsTrue(order.IsCompleted); 
} 

Next Steps

Now that you know how a simple public class with public members can be tested using JustMock, go ahead and check the next topic of the Getting Started series to learn about the numerous features and scenarios you can easily setup and test. In the Create Mock Instances topic, you will learn how to obtain mocked instances of different implementations.

See Also

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