Chapter 12 Prototyping and Testing

1. Chapter 12Prototyping and Testing Design of Biomedical Devices and Systems By Paul H. King Richard C. Fries

2. Prototyping • Hardware • Easily modified and extensible model of a system, including location of individual hardware components. • Software • Easily modified and extensible model (representation, simulation or demonstration) of a planned software system, likely including its interface and input/ output functionality.

3. Prototyping: Hardware • Present to customers for reaction to design • Size correct for application? • Components placed for ease of use? • Wood, foam, cardboard

4. Prototyping: Software • Sometimes used to precede hardware models • Functioning example of final product • Determines if it satisfies the customer’s needs early in process • Allow testing of changes in processes prior to actual implementation of changes

5. Prototypes: Types • Low-Fidelity • High-Fidelity • Exploratory • Experimental • Operational • Horizontal • Vertical • Diagonal • Global • Local A prototype of the entire system; an expanded horizontal prototype that models a greater number of features and covers multiple levels of the system’s structure chart A prototype of a single usability-critical system component; a vertical prototype that is focused on one feature A set of screens that provide a dynamic, computerized, working model of the planned system A throw-away prototype used to clarify project goals, to identify requirements, to examine alternative designs, or to investigate a large and complex system A prototype used to validate system specifications An iterative prototype that is progressively refined until it becomes the final system A prototype that models many features but with little detail; a horizontal slice of a system’s structure chart from the top down to a specific depth most useful in the early stages of design A prototype that models few features but with much detail; a vertical slice of a system’s structure chart from top to bottom; most useful in the later stages of design A prototype that is horizontal down to a particular level, then vertical below that point A set of drawings (e.g., storyboard) that provide a static, non-computerized, non-working mock-up of user interface for the planned system

6. Prototype: Process • Build low-fidelity prototype • Re-specify, re-design, re-evaluate • Freeze these specifications • Finish building the product

7. Testing • Subjecting a device to conditions that indicate its weaknesses, behavior characteristics, and modes of failure. • Ultimate goal: satisfied customer

8. Testing: 3 Basic Reasons • Basic Information • Includes vendor evaluation, vendor comparison, and component limitability • Verification • Process of evaluating the products of a given phase to correctness and consistency with respect to the products and standards provided as input to that phase • Validation • Process of evaluating a product to ensure compliance with specified and implied requirements

9. Testing: Defined • Establishing confidence that a device does what it is supposed to do • The process of operating a device with the intent of finding errors • Detecting specification errors and deviations from the specification • Verifying that a system satisfies its specified requirements or identifying differences between expected and actual results • The process of operating a device or component under specified conditions, observing or recording the results, and making an evaluation of some aspect of the system or component

10. Verification Validation Black Box White Box Hardware Testing Software Testing Functional Testing Robustness Testing Stress Testing Safety Testing Regression Testing Test: Types

11. Stress Testing • Designed to ascertain how the product reacts to a condition in which the amount or rate of data exceeds the amount or rate expected. • Help determine margin of safety that exists • Include Duration and Worst Case Scenario

12. Black Box • Verifies that the end-user requirements are met from the end-user’s point of view • Performed without any knowledge of internal structure • Tester is only interested in finding circumstances in which the device or program does not behave according to its specification.

13. Determining Sample Size and Test Length • MTBF (Mean Time Between Failure) • Basic measure of reliability for repairable items • (sample size)(test time) = MTBF goal (X2α;2r+2)/2 • Example: Calculate the test time for a device that has an estimated MTBF of 20 per million hours if you have only fifteen units to test. List your assumptions.