Chapter 12 Prototyping and Testing

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Chapter 12Prototyping and Testing

• Design of Biomedical Devices and Systems
• By
• Paul H. King
• Richard C. Fries

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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.

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Prototyping Hardware

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

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Prototyping Software

• Sometimes used to precede hardware models
• Functioning example of final product
• Determines if it satisfies the customers needs
  early in process
• Allow testing of changes in processes prior to
  actual implementation of changes

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Prototypes Types

• Low-Fidelity
• High-Fidelity
• Exploratory
• Experimental
• Operational
• Horizontal
• Vertical
• Diagonal
• Global
• Local

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 systems
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 systems
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 prototype of the entire system an expanded
horizontal prototype that models a greater number
of features and covers multiple levels of the
systems structure chart
A prototype of a single usability-critical system
component a vertical prototype that is focused
on one feature
A set of drawings (e.g., storyboard) that provide
a static, non-computerized, non-working mock-up
of user interface for the planned system
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Prototype Process

• Build low-fidelity prototype
• Re-specify, re-design, re-evaluate
• Freeze these specifications
• Finish building the product

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Testing

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

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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

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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

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Test Types

• Verification
• Validation
• Black Box
• White Box
• Hardware Testing
• Software Testing

• Functional Testing
• Robustness Testing
• Stress Testing
• Safety Testing
• Regression Testing

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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

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Black Box

• Verifies that the end-user requirements are met
  from the end-users 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.

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Determining Sample Size and Test Length

• MTBF (Mean Time Between Failure)
• Basic measure of reliability for repairable items
• (sample size)(test time) MTBF goal (X2a2r2)/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.

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