Faking it

Faking ItIsolating Dependencies with Microsoft Fakes

Agenda

Introducing Fakes The Basics Using Stubs Using Shims Advanced Configuration Final Notes Resources

Introducing Fakes

What is it? Where did it come from?

Introducing Fakes

Stub Types

Inheritance based Used when testing a defined contract

Introducing Fakes

Shim Types

Let me start by saying Shims are evil. But they are evil by design. They let you do things you otherwise couldn’t do, which is very powerful. They let you do things you might not want to do, and might know you shouldn’t do, but because of the real world of software, you have to do.

Peter ProvostProgram Manager LeadVisual Studio ALM Tools

Introducing Fakes

Shim Types

Use a profiler to rewrite existing method bodies

Detour virtually any .NET method Performance issues due to the

profiler

The Basics

No additional installation required Isolation type generation driven

by .fakes file Microsoft.QualityTools.Testing.Fakes

assembly/namespace

The Basics

Delegation

Delegates are used to provide the faked functionality

Custom delegate types including support for out and ref parameters

Static class: Microsoft.QualityTools.Testing.Fakes.FakesDeleg

ates

The Basics

Delegation

Overloaded Delegate Types

Action OutAction OutOutAction RefAction RefRefAction

Func OutFunc OutOutFunc RefFunc RefRefFunc

The Basics

Naming

Isolation types are placed in a .Fakes namespace Stub types are prefixed with “Stub” Shim types are prefixed with “Shim” Method parameter types are appended to the

method name “Get” or “Set” is appended to property names

Setters also include parameter type names (like methods)

Generic type arguments are appended to the method name for generic methods

Constructors have parameter type names appended to “Constructor”

Using Stubs

Methods

Assign a delegate to the field that corresponds to the member being isolated

Using Stubs

Properties

Same process as methods Get and Set can be assigned

individually AttachBackingFieldTo[PropertyName]

convenience method

Using Stubs

Events

The framework generates a public method to invoke events [EventName]Event

Using Stubs

Partial Stubs

Allow calling the base implementation when a delegate is not set for a member

Using Stubs

Behaviors

Control what happens when a delegate has not been provided for a member

Set through the InstanceBehavior property

Using Stubs

Stubs Demo

Using Shims

Shim Structure

Shim properties for static members are static on the shim type

Static AllInstances property for applying delegates to all instances of the shim type

Instance properties for applying delegates to a single instance

Using Shims

Instrumentation

ShimsContext Sets up the shim under the IntelliTrace

profiler ShimsContext.Create()

Using Shims

Differences From Stubs

Events don’t have a method to invoke Properties representing the Add and

Remove operations are provided instead Base type members aren’t directly

accessible Static constructors are “shimmable” Bind method for each interface

implemented by the shimmed type Behaviors are controlled by

ShimBehaviors

Using Shims

Shims Demo

Advanced Configuration

Controlling Type Generation Strong Name Signing

Advanced Configuration

Controlling Type Generation

Generating the isolation types is expensive and will extend build time

Configure through the .fakes file Filtering

Advanced Configuration

Controlling Type Generation

Filtering: AttributesAttribute Type Stubs? Shims?

AbstractClasses Boolean ü

FullName String ü ü

Interfaces Boolean ü

Namespace String ü ü

Obsolete* Boolean ü ü

TypeName String ü ü

* Applies only to Remove elements

Advanced Configuration

Controlling Type Generation

Filtering: Matching Tokens

! forces an exact, case sensitive match

* matches the beginning of the string

Advanced Configuration:

Strong Name Signing

Fakes assemblies will be signed with the same key as the underlying assembly unless otherwise specified

Compilation element’s KeyFile attribute in .fakes file

Final Notes

Beware the Docs! Notable Changes from Moles

Notable Changes from Moles Configured through .fakes file rather than .moles Namespace and assembly are .Fakes rather

than .moles Mole types are now shim types Stub prefix is “Stub” rather than “S” Shim prefix is “Shim” rather than “M” ShimsContext replaces HostTypeAttribute Automatic properties can be isolated! Moles allowed for erasing static constructors and

finalizers. Fakes allows shimming static constructors but has no support for finalizers

Moles could control the bitness of the profiler “classes” filter attribute was removed

Resources

Isolating Unit Test Methods with Microsoft Fakeshttp://bit.ly/KYMkyX

Moles Isolation Framework for .NEThttp://bit.ly/LebqZ2

Going Underground: Microsoft Moleshttp://bit.ly/y66D5C