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Mocking Framework Examples

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As a companion to my blog series on .NET Mocking Frameworks and how they work, this repository attempts to implement the same unit tests with mocks using each of the major mocking frameworks available for .NET.

This project is intended to be a reference for anyone looking to compare .NET mocking frameworks or see syntax examples for a given framework. It is not intended to be an exhaustive reference, not is it gauranteed to be bug-free (but please do let me know if you find any issues).

Code Under Test

In order to write tests, we need some code in need of testing. Thus, I've created the LunchNotifier, a slightly-more-than-hello-world class against which unit tests (with mocks) can be written.

The Pretext

One of the benefits provided to Stack Overflow emplpoyees working in the New York office is free lunch from in-house chefs. Every day, when the cooks have completed preparing the meal, a notification goes out to employees in the office to let them know food is available.

CodeBeingTested Project

In the CodeBeingTested project, the LunchNotifier class is our main target.

This class takes has five external dependancies that need to be mocked in order to perform our tests:

  • INotificationService (injected via constructor)
    • implements the actual notification actions, interfacing with external notification platforms like email or Slack
  • ILogger (injected via constructor)
    • provides ability to log messages for debugging/troubleshooting
  • IEmployeeService (injected via constructor)
    • used to get a list of employees (as IEmployee objects) based in the New York Office
  • IEmployee (returned from IEmployeeService)
    • encapsulates employee-specific logic and data
  • System.DateTime
    • the logic will send a different notification template based on the time of day

The main logic is in LunchNotifier.SendLunchtimeNotifications(). This method includes an inline call to System.DateTime.Now, which is not mockable by contrained frameworks like Moq or RhinoMocks:

public void SendLunchtimeNotifications()
{
	var now = DateTime.Now;
	var templateToUse = now.Hour > 12 ? LateLunchTemplate : RegularLunchTemplate;

An alternate implementation is provided for use by contrained frames in LunchNotifier.SendLunchtimeNotifications_DateTimeSeam(), where the call to DateTime.Now has been extracted into it's own method, which can be replaced in a mock:

public virtual DateTime GetDateTime() => DateTime.Now;

public void SendLunchtimeNotifications_DateTimeSeam()
{
    var now = GetDateTime();
    var templateToUse = now.Hour > 12 ? LateLunchTemplate : RegularLunchTemplate;

Sample Projects and Tests

Each of the remaining projects attempt to implement a similar set of unit tests against the LunchNotifier using different Mocking Frameworks.

All tests are written using NUnit v3.10 by way of NuGet package.

In some cases, there are multiple ways to approach a test using the mocking framework, so I have provided multiple variants of the test to showcase the different approaches.

Test: Test_EmployeeInOfficeGetsNotified

This test creates a mock employee "Bob" who prefers Email notifications and uses mocks to ensure the LunchNotifier logic will send him an email when lunch is ready.

Test: Test_ExceptionDoesNotStopNotifications

This test creates two mock employees, "Bob" and "Martha" and ensures that if sending a notification to one of them results in the error getting logged and does not prevent the remaining employees from getting notified.

Test: Test_CorrectTemplateIsUsed_LateLunch

This test uses NUnit's TestCase syntax to run two test cases, one for before 1pm and one for after 1pm, to ensure the appropriate notification template is used based on the time of day.

For unconstrained frameworks, DateTime.Now can be directly controlled to return the test's input time, however, constrained frameworks cannot, so they must extract the call to DateTime.Now into a sperate method and modify that new method's behavior instead. Thus the need for the SendLunchtimeNotifications_DateTimeSeam variant.

Frameworks Used

Moq

Type: Constrained

Project: https://github.com/Moq/moq4/wiki/Quickstart

NuGet: https://www.nuget.org/packages/moq/

RhinoMocks

Type: Constrained

Project: https://github.com/hibernating-rhinos/rhino-mocks

NuGet: https://www.nuget.org/packages/RhinoMocks

WARNING: RhinoMocks is effectively a dead project and will likely not provide support for future changes in .NET, such as .NET Core. I do not suggest you begin using this framework if you're not already using it.

To run these tests, you must have VS2017 Enterprise (or equiv) installed.

NSubstitute

Type: Constrained

Project: http://nsubstitute.github.io/

NuGet: https://www.nuget.org/packages/NSubstitute

Microsoft Fakes

Type: Unconstrained

Microsoft Fakes comes as part of Visual Studio 2017 Enterprise or Visual Studio 2015 Ultimate and is not available as a sperate component.

Fakes does not natively support the AssertWasCalled style validation, so I utilize an additional NuGet package (which I have contributed to) to provide that feature: Fakes.Contrib / NuGet

Typemock Isolator

Type: Unconstrained

Product Info: https://www.typemock.com/isolator

This product requires a paid license (there's a free 15-day trial available) to do unconstrained mocking. Typemock was nice enought to provide me with a free community license so that I can work on projects like this one.