---
title: "Preview: Placeholder arguments and custom argument checkers"
url: "https://osherove.com/blog/2009/4/2/preview-placeholder-arguments-and-custom-argument-checkers.md"
canonical: "https://osherove.com/blog/2009/4/2/preview-placeholder-arguments-and-custom-argument-checkers.html"
published: "2009-04-02T05:50:32"
updated: "2009-04-02T05:50:32"
tags: [".NET", "Agile", "Typemock", "Unit Testing"]
author: "Roy Osherove"
description: "here is a glimpse of the feature the guys are working on at the moment. I call it “Placeholder Arguments”. It’s a variation of the “how do you allow the user to check parameters passed to a method?” question when…"
usage: "Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page)."
license: "https://creativecommons.org/licenses/by/4.0/"
---

# Preview: Placeholder arguments and custom argument checkers

By Roy Osherove April 2, 2009 In [.NET](https://osherove.com/blog/category/net), [Agile](https://osherove.com/blog/category/agile), [Typemock](https://osherove.com/blog/category/typemock), [Unit Testing](https://osherove.com/blog/category/unit-testing)

**Historical article** · Originally published April 2, 2009; technical details may be outdated.

here is a glimpse of the feature [the guys](http://www.typemock.com/) are working on at the moment. I call it “Placeholder Arguments”. It’s a variation of the **“how do you allow the user to check parameters passed to a method?”** question when working with isolation frameworks. We implemented a [suggestion from Vagif Abilov](http://bloggingabout.net/blogs/vagif/archive/2009/03/12/how-i-would-match-faked-method-s-arguments-if-i-was-typemock-isolator.aspx), one of our Typemock Insiders.

The idea is pretty elegant, really – allow the user to define (inside the lambda expression) ”placeholder” arguments, that can then be checked in a custom delegate provided by the user. Then, you can call the method with a combination of “real” and “placeholder” arguments, and “real” ones will not be checked by default. Only the placeholder ones can then be used in the custom argument matcher the user provides.

This should be out in the coming weeks.

![image](https://osherove.com/img/wb/e0dd859b_weblogs.asp.net_blogs_rosherove_image_thumb_3D0EAC6D.png)

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---

## About the author

**Roy Osherove**: Senior Solutions Architect at AWS working on AI for production and AI-driven development; author of The Art of Unit Testing and Elastic Leadership, with about 20 years of consulting and training on unit testing, TDD, team leadership and continuous delivery.

### Sites

- [RobotPaper](https://robotpaper.ai/): This blog: AI patterns and anti-patterns, AI and coding agents, and engineering leadership.
- [osherove.com](https://osherove.com): Roy's personal site. Author of The Art of Unit Testing and Elastic Leadership; consulting and training on unit testing, TDD, team leadership and continuous delivery, plus about 20 years of blog posts.
- [The Art of Unit Testing](https://www.artofunittesting.com): The Art of Unit Testing, 3rd Edition (Manning): readable, maintainable, trustworthy unit tests, plus TDD workshops in C#, JavaScript, Java and Kotlin.
- [5whys.com](https://www.5whys.com): Roy's writing on software team leadership: self-organizing teams, surviving chaos, learning mode and the Elastic Leadership model.
- [Pipeline Driven](https://pipelinedriven.org): Continuous delivery and DevOps practices: build patterns, pipeline-friendly testing, DevOps metrics and enterprise DevOps.
- [Elastic Leadership](https://www.elasticleadership.com): Elastic Leadership, Roy's framework for software team leaders (survival, learning and self-organizing modes).

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### License

Licensed under CC BY 4.0 — reuse, quote and adapt with attribution (Roy Osherove, link to the original page). License: https://creativecommons.org/licenses/by/4.0/