Swapping One Object's Implementation With Another

You can swap one object implementation with another by using the Swap.CallsOn(Object obj).
When a method is called on the swapped object, it is replaced with a corresponding implementation (a method with the same signature) on the swapping object.
This means that the swapped object will start behaving like the object it was swapped with for all methods they have in common.

Syntax

C#

  Isolate.Swap.CallsOn(Object).WithCallsTo(Object);

VB

 Isolate.Swap.CallsOn(logger).WithCallsTo(swapped)

Samples

Sample 1: Swapping a real object

C#

[TestMethod]
public void SwapLoggerWithSwapped()
{
    // Create the object under test
    RealLogger logger = new RealLogger();
    // Create the object calls will be redirected to
    TestLogger swapped = new TestLogger();

    // Redirect any calls from the object under test to the swapping target
    Isolate.Swap.CallsOn(logger).WithCallsTo(swapped);

    // logger.Write() is redirected to TestLogger.Write() which writes to console instead of throwing exception
    logger.Write("Hello World");

    // We can still verify the call to logger.Write() happened
    Isolate.Verify.WasCalledWithAnyArguments(() => logger.Write(""));
}

public class RealLogger
{        
    public void Write(string toWrite)
    {
        //logFile.WriteAllText(logFilePath, toWrite);
        throw new NotImplementedException();
    }
}

public class TestLogger
{
    public void Write(string toWrite)
    {
        Console.WriteLine("RealLogger.Write() was called with {0}", toWrite);
    }
}

VB

<TestMethod()> 
Public Sub SwapLoggerWithSwapped()
    ' Create the object under test
    Dim logger As New RealLogger()
    ' Create the object calls will be redirected to
    Dim swapped As New TestLogger()

    ' Redirect any calls from the object under test to the swapping target
    Isolate.Swap.CallsOn(logger).WithCallsTo(swapped)

    ' logger.Write() is redirected to TestLogger.Write() which writes to console instead of throwing exception
    logger.Write("Hello World")

    ' We can still verify the call to logger.Write() happened
    Isolate.Verify.WasCalledWithAnyArguments(Sub() logger.Write(""))

End Sub

Public Class RealLogger
    Public Sub Write(toWrite As String)
        'logFile.WriteAllText(logFilePath, toWrite);
        Throw New NotImplementedException()
    End Sub
End Class

Public Class TestLogger
    Public Sub Write(toWrite As String)
        Console.WriteLine("RealLogger.Write() was called with {0}", toWrite)
    End Sub
End Class

Sample 2: Swapping a future faked object

You can also use the CallsOn method when you wish to swap a future faked object.

C#

[TestMethod]
public void SwapFakedLoggerWithSwapped()
{
    // Create the faked object
    var loggerHandle = Isolate.Fake.NextInstance<RealLogger>();
    // Create the object calls will be redirected to
    TestLogger swapped = new TestLogger();

    // Redirect any calls from the object under test to the swapping target
    Isolate.Swap.CallsOn(loggerHandle).WithCallsTo(swapped);

    // loggerHandle.Write() is redirected to TestLogger.Write() which writes to console instead of throwing exception
    RealLogger fakeLogger = new RealLogger();
    fakeLogger.Write("Hello World");

    // We can still verify the call to loggerHandle.Write() happened
    Isolate.Verify.WasCalledWithAnyArguments(() => loggerHandle.Write(""));
}

public class RealLogger
{        
    public void Write(string toWrite)
    {
        //logFile.WriteAllText(logFilePath, toWrite);
        throw new NotImplementedException();
    }
}

public class TestLogger
{
    public void Write(string toWrite)
    {
        Console.WriteLine("RealLogger.Write() was called with {0}", toWrite);
    }
}

VB

<TestMethod()> 
Public Sub SwapFakedLoggerWithSwapped()
    ' Create the object under test
    Dim loggerHandle = Isolate.Fake.NextInstance(Of RealLogger)()
    ' Create the object calls will be redirected to
    Dim swapped As New TestLogger()

    ' Redirect any calls from the object under test to the swapping target
    Isolate.Swap.CallsOn(loggerHandle).WithCallsTo(swapped)

    ' loggerHandle.Write() is redirected to TestLogger.Write() which writes to console instead of throwing exception
    Dim fakeLogger As New RealLogger()
    fakeLogger.Write("Hello World")

    ' We can still verify the call to loggerHandle.Write() happened
    Isolate.Verify.WasCalledWithAnyArguments(Sub() loggerHandle.Write(""))

End Sub

Public Class RealLogger
    Public Sub Write(toWrite As String)
        'logFile.WriteAllText(logFilePath, toWrite);
        Throw New NotImplementedException()
    End Sub
End Class

Public Class TestLogger
    Public Sub Write(toWrite As String)
        Console.WriteLine("RealLogger.Write() was called with {0}", toWrite)
    End Sub
End Class