Returns
The Returns method is used with non void calls to ignore the actual call and return a custom value. This topic goes through a number of scenarios where the Returns method is useful. For them, we will be using the following interface:
public interface IFoo
{
int Bar { get; set; }
int Echo(int myInt);
int Execute(int myInt1, int myInt2);
}
Public Interface IFoo
Function Execute(ByVal int1 As Integer, ByVal int2 As Integer)
Property Bar As Integer
Function Echo(ByVal int As Integer) As Integer
End Interface
You may additionally want to check theCreate Mocks By Example article.
Assert Property Get Call
With Returns method you can change the return value from a property get call.
[TestMethod]
public void ShouldAssertPropertyGetCall()
{
// Arrange
var foo = Mock.Create<IFoo>();
Mock.Arrange(() => foo.Bar).Returns(10);
// Act
var actual = 0;
actual = foo.Bar;
// Assert
Assert.AreEqual(10, actual);
}
<TestMethod()>
Public Sub ShouldAssertPropertyGetCall()
' Arrange
Dim foo = Mock.Create(Of IFoo)()
Mock.Arrange(Function() foo.Bar).Returns(10)
' Act
Dim actual = 0
actual = foo.Bar
' Assert
Assert.AreEqual(10, actual)
End Sub
In this example we arrange the Bar property get to return 10 when called. By acting with actual = foo.Bar; we assign 10 to actual, as foo.Bar will result in 10. Finally, a verification is asserted.
Assert Method Call with Matcher
A common case is to mock a method call to return a custom value in conjunction with a matcher.
[TestMethod]
public void ShouldAssertMethodCallWithMatcher1()
{
// Arrange
var foo = Mock.Create<IFoo>();
Mock.Arrange(() => foo.Echo(Arg.IsAny<int>())).Returns((int i) => ++i);
// Act
var actual = foo.Echo(10);
// Assert
Assert.AreEqual(11, actual);
}
<TestMethod()>
Public Sub ShouldAssertMethodCallWithMatcher1()
' Arrange
Dim foo = Mock.Create(Of IFoo)()
Mock.Arrange(Function() foo.Echo(Arg.IsAny(Of Integer)())).Returns(Function(i As Integer) System.Threading.Interlocked.Increment(i))
' Act
Dim actual = foo.Echo(10)
' Assert
Assert.AreEqual(11, actual)
End Sub
Here we use an Arg.IsAny matcher for the call to match calls to foo.Echo with any int argument. In the Returns method, instead of using a simple int value, we use a function to return the passed value incremented with 1.
You may also use a more complicated matcher. For example, you can make arrangement for passing exactly 10 to Echo method. With the following line of code we return exactly what has been passed:
[TestMethod]
public void ShouldAssertMethodCallWithMatcher2()
{
// Arrange
var foo = Mock.Create<IFoo>();
Mock.Arrange(() => foo.Echo(Arg.Matches<int>(x => x == 10))).Returns((int i) => i);
// Act
var actual = foo.Echo(10);
// Assert
Assert.AreEqual(10, actual);
}
<TestMethod()>
Public Sub ShouldAssertMethodCallWithMatcher2()
' Arrange
Dim foo = Mock.Create(Of IFoo)()
Mock.Arrange(Function() foo.Echo(Arg.Matches(Of Integer)(Function(x) x = 10))).Returns(Function(i As Integer) i)
' Act
Dim actual As Integer = foo.Echo(10)
' Assert
Assert.AreEqual(10, actual)
End Sub
The following example mocks the Execute method so that it returns its second argument. We use lambda expression in the Returns body to select the desired argument. After we have arranged we act by calling foo.Execute(100, 10) and verify that it has returned actually what we expect, namely 10. Additionally, we verify that a call with any int as first argument and exactly 10 as second has been made.
[TestMethod]
public void ShouldReturnWhateverSecondArgIs()
{
// Arrange
var foo = Mock.Create<IFoo>();
Mock.Arrange(() => foo.Execute(Arg.IsAny<int>(), Arg.IsAny<int>())).Returns((int id, int i) => i);
// Act, Assert
Assert.AreEqual(foo.Execute(100, 10), 10);
Mock.Assert(() => foo.Execute(Arg.IsAny<int>(), Arg.Matches<int>(x => x == 10)));
}
<TestMethod()>
Public Sub ShouldReturnWhateverSecondArgIs()
' Arrange
Dim foo = Mock.Create(Of IFoo)()
Mock.Arrange(Function() foo.Execute(Arg.AnyInt, Arg.AnyInt)).Returns(Function(id As Integer, i As Integer) i)
' Act, Assert
Assert.AreEqual(foo.Execute(100, 10), 10)
Mock.Assert(Sub() foo.Execute(Arg.AnyInt, Arg.Matches(Of Integer)(Function(x) x = 10)))
End Sub
Refer to the Matchers help topic for more information about using matchers.
Executing Mocked Method In Same Test Method
Assume we have the following class:
public class Foo
{
public int Echo(int myInt)
{
throw new NotImplementedException();
}
}
Public Class Foo
Public Function Echo(num As Integer) As Integer
Throw New NotImplementedException
End Function
End Class
JustMock supports executing mocked method in same test method without necessarily passing the type as an argument.
[TestMethod]
public void ShouldExecuteMockForSameInstanceInSameContext()
{
// Arrange
var foo = Mock.Create<Foo>();
Mock.Arrange(() => foo.Echo(Arg.AnyInt)).IgnoreInstance().Returns((int arg1) => arg1);
// Assert
Assert.AreEqual(new Foo().Echo(10), 10);
}
<TestMethod()>
Public Sub ShouldExecuteMockForSameInstanceInSameContext()
' Arrange
Dim foo = Mock.Create(Of Foo)()
Mock.Arrange(Function() foo.Echo(Arg.AnyInt)).IgnoreInstance().Returns(Function(arg1 As Integer) arg1)
' Assert
Assert.AreEqual(New Foo().Echo(10), 10)
End Sub
In this example, Echo is called on a new Foo instance, instead of a mocked one. However, the arrangement is applied.