Factory Acceptance Testing 101: Preparing for Customer Buy-Off

Factory Acceptance Testing (FAT) is a critical milestone when designing turnkey systems. It is the last opportunity to test a system prior to shipment to its final location.

This article walks through the fundamentals of FAT, how it differs from other testing phases, and how to prepare your system and your customer for a smooth buy-off.

Background

Before we dive into the topic of Factory Acceptance Testing, I want to outline an example of the Project Process DMC follows. After thousands of projects, DMC has found that a phased approach is the best way to make a system production-ready.

• Requirements & Specifications – DMC works collaboratively with the client to determine system requirements. This phase often culminates in a “System Functional Review.”
• Preliminary Design – DMC defines a Preliminary Design as a ~20% complete design, where the high-level architecture has been mapped out and identified risks have been evaluated to the point where a plan is in place. This phase often culminates in a “Preliminary Design Review.”
• Comprehensive Design – DMC defines a Comprehensive Design as an ~80% complete design, with the remaining tasks to be finalized during the Development & Fabrication phases. (i.e., what nuts and bolts will be used to mount the hardware). This phase often culminates in a “Critical Design Review.”
• Development – The software development portion of the implementation phase, where any custom software is created and tested.
• Fabrication – The hardware build portion of the implementation phase, where any hardware is assembled into a complete system.
• Factory Acceptance Testing – The point in the project process where DMC validates the system prior to shipping it to the client site.
• Site Acceptance Testing – The final validation testing performed after the system arrives at the client site.
• Training & Support – After delivery and acceptance, DMC can provide training on using or extending the system, as well as support for troubleshooting and future improvements.

If you want to learn more about DMC’s Project Management that makes this flow happen, you can find more details here.

Project Specific Customizations

At DMC, we understand that not all projects are the same, so the Project Phases are customized on an individual project level.

• If a customer already has a well-defined Requirement & Specification document, we can jump straight into the Design phases.
• For small projects, we might combine “Requirement & Specification, Preliminary Design, and Comprehensive Design” into a single “Design” phase.
• For software-only projects, we remove the Fabrication phase and may combine “Factory Acceptance Testing and Site Acceptance Testing” into a single “Testing” phase.

Now that we have a better understanding of DMC’s typical project process, let’s talk about how we can prepare for a successful Factory Acceptance Testing phase.

FAT vs. SAT vs. ATP: What’s the Difference?

Before we dive into any details, let’s define terms that will be used in this blog.

Factory Acceptance Testing (FAT)

FAT is testing at the fabrication location to verify that the system meets the agreed-upon requirements before shipment. FAT focuses on testing that can be performed without the systems or hardware only available at the customer’s facility.

Site Acceptance Testing (SAT)

SAT is a test conducted after the system has been installed at the customer’s facility and is the first opportunity to test with systems or hardware only available at the site. SAT will often repeat tests performed during FAT to ensure the system wasn’t damaged during transport.

Acceptance Test Plan (ATP)

The ATP is the test plan used to execute FAT or SAT. It defines what is tested, how it is tested, and what constitutes a pass or fail. A well-written ATP is essential for efficient execution and clear customer sign-off.

What Does a Successful FAT Look Like?

FAT is successful when all parties are in agreement that the system meets its requirements and is ready for shipment to its final location.

How Do We Ensure FAT Is Successful?

Preparation is critical to ensuring that FAT is an efficient and productive use of time. We will dive a little deeper into how we can maximize testing prior to FAT, define participation and roles during FAT, and how to develop the ATP.

What Testing Should Occur Before FAT?

FAT should not be the first time testing occurs during the project process. Systems and code should be tested as they are developed. Testing strategy is a huge topic and will not be discussed further in this blog.

Who Participates During FAT?

At DMC, customer involvement during the FAT process is highly encouraged. At the end of the day, the customer will own and operate the system, so DMC strives to include the customer in as many aspects of our project process as possible. Some benefits of customer involvement during FAT are:

• A chance to make tweaks to the system without major cost or schedule impacts to the project.
• An opportunity to receive hands-on training with the team that developed the system.
• Provides an opportunity to identify gaps or misunderstandings in requirements.

Regardless of whether or not the customer attends FAT, they should be involved in developing the ATP. Ideally, either DMC or the client would write the acceptance test plan, while the other reviews and approves.

Typically, the customer should be responsible for writing the acceptance test plan to ensure complete test coverage and feel comfortable accepting the system at the end of the day. However, DMC engineers are experts and will often develop the ATP.

How Do You Develop an ATP?

Each item in an ATP should be clear, repeatable, and objective. In order to achieve this goal, each test should have the following core elements at a minimum:

• Test Procedure: Step-by-step instructions
• Acceptance Criteria: Objective pass/fail conditions
• Observed Results: What actually occurred
• Result Files: Logs, screenshots, or data files as evidence

Depending on your specific requirements, you can also consider tracking the Test Type, Test Operator, Test Date, and the approval status of Individual Results. If you’re looking for more information on why you might need an ATP, check out this blog.

Does the Order of ATP Execution Matter?

The order of individual ATP items is crucial for reducing the amount of time spent troubleshooting and debugging the system. The highest system-level impact should come first, followed by more narrowly scoped items. This narrows down potential causes of issues, reducing the overall time spent troubleshooting and debugging the system.

As you test systems and subsystems, start with the simplest components and add more complex capabilities sequentially.

A high-level concept for ATP Execution Order is as follows:

Conclusion

Factory Acceptance Testing is more than a checkbox. By involving the customer early, planning FAT thoughtfully, and executing against a clear, well-structured ATP, teams can streamline buy-off, minimize rework, and set the project up for long-term success.