Mocking .NET Without Hurting Its Feelings (Stack Overflow Team Meetup 2017)

Mocking .NET Without Hurting Its Feelings

class DependenciesHog

{

public string foo

{

get;

set;

}

private void bar(int x)

{

//I do stuff

}

public event BigEvent EventHorizon;

private void SpaceFiller()

{

while (true)

{

LookInteresting();

}

}

}

Why use a Mocking Framework?

Using Hand-Crafted, Artisanal Mocks

John M. Wright

john@wrightfully.com

@wright2tweet

mock

What can they do?

mock.VerifyAllExpectations();

mock.AssertWasCalled(x => x.MyMethod());

mock

vs

stub

vs

stub

A rose by any other name

would smell as sweet

work about the same

www.wrightfully.com

mock types

© Copyright 2017 John M. Wright

How do they do it?

Per Dev:

Per 5 Build Servers:

A Matter of Syntax

Code Examples (aka: What can you do?)

Unconstrained Code Examples

Generating Mocks

Example Test using a Mock

Code being tested

Using Moq Syntax

Code being tested

Unconstrained Frameworks:

Make Your Own Man-In-The-Middle Attack

Constrained Frameworks:

Limitations of Class Inheritance

Constrained Frameworks:

Class Inheritance On-Demand

internal types & members

Mocking Internal Types/Members

AssemblyInfo.cs

[assembly: InternalsVisibleTo("Your.TestAssembly")]

[assembly: InternalsVisibleTo("DynamicProxyGenAssembly2, PublicKey=0024000004800000940000000602000000240000525341310004000001000100c547cac37abd99c8db225ef2f6c8a3602f3b3606cc9891605d02baa56104f4cfc0734aa39b93bf7852f7d9266654753cc297e7d2edfe0bac1cdcf9f717241550e0a7b191195b7667bb4f64bcb8e2121380fd1d9d46ad2d92d2d15605093924cceaf74c4861eff62abf69b9291ed0a340e113be11e6a7d3113e92484cf7045cc7")]

sealed types

Generated Classes:

• Inherit / Extend Mocked Type
• Override virtual/abstract members
• Check for configured stubs/mocks
• Save details for later verification
• Take action based on configuration

Code Examples (aka: What can you do?)

ICorProfilerInfo::

SetILFunctionBody

Hijacked Code:

• Can change Behavior of ANY Type/Member
• Doesn't rely on inheritance
• Everything gets JIT'd, so anything can be mocked!
• Injected code will:
• Check for configured stubs/mocks
• Save details for later verification
• Take action based on configuration