Controlling Live Objects Behavior

Faking Behavior for Live Objects

A live object is a test object which has been instantiated normally, and not through the AAA mechanisms (see creating fake objects). When it's only desired to modify a test object's behavior for a specific method call, it is useful to use a live object and alter only the specific behavior rather than create a new fake object using Isolate.Fake.Instance().

Example:

RealLogger logger = new RealLogger(); // this is a normal "live" object
Isolate.WhenCalled(() => logger.Log("message")).IgnoreCall(); // ignore only the Log method

When altering behavior for live objects, only the method(s) being changed will be impacted. All other methods will continue to return their original implementations. This is similar to creating a fake object using the Members.CallOriginal setting.

The same principals apply to changing behavior for specific static methods without first using Isolate.Fake.StaticMethods (see faking static method behavior). When a static method for a type is being altered like this, all other static methods will continue to work normally.

Example:

Isolate.WhenCalled(() => LoggerFactory.GetLogger()).WillThrow(new OutOfMemoryException());

live objects and static behavior faking work also for non-public calls (see non-public faking) through the Isolate.NonPublic.WhenCalled() entry point for methods, Isolate.NonPublic.Property for properties and Isolate.NonPublic.Indexer for index calls.

Example:

RealLogger logger = new RealLogger();
Isolate.NonPublic.Property.WhenGetCalled(logger, "IsDiskFull").WillReturn(true); // faking internal property behavior on real object

Verifying Live Objects Behavior

Live objects support verification just like fake objects (see verifying behavior) with one limitation: it is only possible to verify calls on objects or types (in the case of static methods) which were used (activated) with WhenCalled()

Example:

[TestMethod]
public void Test1()
{
    RealLogger logger = new RealLogger();
    logger.Write("Hello");
    Isolate.Verify.WasCalledWithAnyArguments(() => logger.Write("")); // this verification fails - the live object did not pass through WhenCalled()
}

[TestMethod]
public void Test2()
{
    RealLogger logger = new RealLogger();
    Isolate.WhenCalled(() => logger.Write("")).IgnoreCall();

    logger.Write("Hello");
    Isolate.Verify.WasCalledWithAnyArguments(() => logger.Write("")); // this verification succeed - the live object was 'activated' in the bold line
}