Arrange Act Assert
Arrange/Act/Assert (AAA) is a pattern for arranging and formatting code in Unit Test methods.
It is a best practice to author your tests in more natural and convenient way. The idea is to develop a unit test by following these 3 simple steps:
- Arrange – setup the testing objects and prepare the prerequisites for your test.
- Act – perform the actual work of the test.
- Assert – verify the result.
Benefits of Using Arrange Act Assert
- Clearly separates what is being tested from the setup and verification steps.
- Clarifies and focuses attention on a historically successful and generally necessary set of test steps.
- Makes some test smells more obvious:
- Assertions intermixed with "Act" code.
- Test methods that try to test too many different things at once.
Arrange/Act/Assert with JustMock
Lets illustrate the benefits of the pattern with an example. We will use a sample warehouse and a dependent order object. The warehouse holds inventories of different products. An order contains a product and quantity.
The warehouse interface and the order class look like this:
public delegate void ProductRemoveEventHandler(string productName, int quantity);
public interface Iwarehouse
{
event ProductRemoveEventHandler ProductRemoved;
string Manager { get; set; }
bool HasInventory(string productName, int quantity);
void Remove(string productName, int 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 IsFilled { get; private set; }
public void Fill(Iwarehouse warehouse)
{
if (warehouse.HasInventory(this.ProductName, this.Quantity))
{
warehouse.Remove(this.ProductName, this.Quantity);
}
}
public virtual string Receipt(DateTime orderDate)
{
return string.Format("Ordered {0} {1} on {2}", this.Quantity, this.ProductName, orderDate.ToString("d"));
}
}
Public Delegate Sub ProductRemovedEventHandler(productName As String, quantity As Integer)
Public Interface IWarehouse
Event ProductRemoved As ProductRemovedEventHandler
Property Manager() As String
Function HasInventory(productName As String, quantity As Integer) As Boolean
Sub Remove(productName As String, quantity As Integer)
End Interface
Public Class Order
Public Sub New(productName As String, quantity As Integer)
Me.ProductName = productName
Me.Quantity = quantity
End Sub
Public Property ProductName() As String
Get
Return m_ProductName
End Get
Private Set(value As String)
m_ProductName = value
End Set
End Property
Private m_ProductName As String
Public Property Quantity() As Integer
Get
Return m_Quantity
End Get
Private Set(value As Integer)
m_Quantity = value
End Set
End Property
Private m_Quantity As Integer
Public Property IsFilled() As Boolean
Get
Return m_IsFilled
End Get
Private Set(value As Boolean)
m_IsFilled = value
End Set
End Property
Private m_IsFilled As Boolean
Public Sub Fill(warehouse As IWarehouse)
If warehouse.HasInventory(Me.ProductName, Me.Quantity) Then
warehouse.Remove(Me.ProductName, Me.Quantity)
IsFilled = True
End If
End Sub
Public Overridable Function Receipt(orderDate As DateTime) As String
Return String.Format("Ordered {0} {1} on {2}", Me.Quantity, Me.ProductName, orderDate.ToString("d"))
End Function
End Class
Arrange
First we need an order:
var order = new Order("Camera", 2);
Dim order = New Order("Camera", 2)
Now let’s mock the warehouse:
var warehouse = Mock.Create<IWarehouse>();
Dim warehouse = Mock.Create(Of IWarehouse)()
We want to ensure that when an order of 2 cameras is placed, the warehouse returns that it has enough quantity of the product.
Mock.Arrange(() => warehouse.HasInventory("Camera", 2)).Returns(true);
Mock.Arrange(Function() warehouse.HasInventory("Camera", 2)).Returns(true)
You can also check the Create Mocks By Example topic that demonstrates how you can arrange mock objects in more complex scenarios.
That’s it. We set up the testing objects for our test. Now let’s act.
Act
Fill our order from the warehouse.
order.Fill(warehouse);
order.Fill(warehouse)
Once we have executed the desired action, we need to ensure that it has been completed successfully and our order was actually filled, meaning that the warehouse really had inventory of 2 cameras.
Assert
We will use the Assert class from Microsoft.VisualStudio.TestTools.UnitTesting namespace (found in Microsoft.VisualStudio.QualityTools.UnitTestFramework assembly – automatically added as a reference from Visual Studio while creating a Test Project) to ensure that the IsFilled property of the order is set to true.
Assert.IsTrue(order.IsFilled);
Assert.IsTrue(order.IsFilled)
With this simple example we illustrated the use of the AAA pattern and showed how easy it is to test your code with JustMock. Notice that you don’t need to change even a single line of your original code to set up, execute and verify its correctness.
Verify Interaction
Now let's take it a little further and verify not only the final result, but also the interaction while executing the test.
We arranged that when the warehouse’s HasInventory method is called with specific parameters, it should return true, but we never ensured that this method is actually called. Let's change the Arrange method and mark that warehouse.HasInventory must be called.
Mock.Arrange(() => warehouse.HasInventory("Camera", 2)).Returns(true).MustBeCalled();
Mock.Arrange(Function() warehouse.HasInventory("Camera", 2)).Returns(true).MustBeCalled()
To verify this we need to call Mock.Assert in the Assert phase with the warehouse object.
Mock.Assert(warehouse);
Mock.Assert(warehouse)
Verify Order of Calls
Furthermore you may want to ensure that a set of method calls are executed in a particular order. Let`s assume we have the following IFoo interface:
public interface IFoo
{
void Submit();
void Echo();
}
Public Interface IFoo
Sub Submit()
Sub Echo()
End Interface
You use the Arrange method to define the methods invocation order.
[TestMethod]
public void ShouldVerifyCallsOrder()
{
// Arrange
var foo = Mock.Create<IFoo>();
Mock.Arrange(() => foo.Submit()).InOrder();
Mock.Arrange(() => foo.Echo()).InOrder();
// Act
foo.Submit();
foo.Echo();
// Assert
Mock.Assert(foo);
}
<TestMethod()>
Public Sub ShouldVerifyCallsOrder()
' Arrange
Dim foo = Mock.Create(Of IFoo)()
Mock.Arrange(Sub() foo.Submit()).InOrder()
Mock.Arrange(Sub() foo.Echo()).InOrder()
' Act
foo.Submit()
foo.Echo()
' Assert
Mock.Assert(foo)
End Sub
Again to verify this we need to call Mock.Assert in the Assert phase with the foo object.
Note that the InOrder option also supports asserting the order of mock calls regardless of the instance within the test scope. Imagine that you have to validate that the user has logged in before using their shopping cart in your application.
public interface IUserValidationService
{
int ValidateUser(string userName, string password);
}
public interface IShoppingCartService
{
IList<string> LoadCart(int userID);
}
Public Interface IUserValidationService
Function ValidateUser(ByVal userName As String, ByVal password As String) As Integer
End Interface
Public Interface IShoppingCartService
Function LoadCart(ByVal userID As Integer) As IList(Of String)
End Interface
Here we have defined the IUserValidationService and the IShoppingCartService services whose invocation order we are going to assert in the following test:
[TestMethod]
public void ShouldAssertInOrderForDifferentInstancesInTestMethodScope()
{
string userName = "Bob";
string password = "Password";
int userID = 5;
var cart = new List<string> {"Foo", "Bar"};
// Arrange
var userServiceMock = Mock.Create<IUserValidationService>();
var shoppingCartServiceMock = Mock.Create<IShoppingCartService>();
Mock.Arrange(() => userServiceMock.ValidateUser(userName, password)).Returns(userID).InOrder().OccursOnce();
Mock.Arrange(() => shoppingCartServiceMock.LoadCart(userID)).Returns(cart).InOrder().OccursOnce();
// Act
userServiceMock.ValidateUser(userName, password);
shoppingCartServiceMock.LoadCart(userID);
// Assert
Mock.Assert(userServiceMock);
Mock.Assert(shoppingCartServiceMock);
}
<TestMethod()>
Public Sub ShouldAssertInOrderForDifferentInstancesInTestMethodScope()
Dim userName As String = "Bob"
Dim password As String = "Password"
Dim userID As Integer = 5
Dim cart As IList(Of String) = {"Foo", "Bar"}
' Arrange
Dim userServiceMock = Mock.Create(Of IUserValidationService)()
Dim shoppingCartServiceMock = Mock.Create(Of IShoppingCartService)()
Mock.Arrange(Function() userServiceMock.ValidateUser(userName, password)).Returns(userID).InOrder().OccursOnce()
Mock.Arrange(Function() shoppingCartServiceMock.LoadCart(userID)).Returns(cart).InOrder().OccursOnce()
' Act
userServiceMock.ValidateUser(userName, password)
shoppingCartServiceMock.LoadCart(userID)
' Assert
Mock.Assert(userServiceMock)
Mock.Assert(shoppingCartServiceMock)
End Sub
In the arrange phase we defined that the ValidateUser call should be made only once and before the LoadCart service call. The LoadCart call should also occur only once and should follow the ValidateUser service call. We act and then assert our expectations.
Refer to the Asserting Occurrence topic to learn more about asserting occurrence. The example also uses the Returns option in order to ignore the actual call and return a custom value.