Prototype phase (“Wizard of Oz” testing)

The goal of this phase is to create a prototype of the application, leaving the design flexible enough to accommodate changes in prompts and dialog flow in subsequent phases of the design.

For the first iteration, you may want to use a technique known as “Wizard of Oz” testing. This technique can be used before you begin coding, as it requires only a prototype paper script and two people: one to play the role of the user, and a human “wizard” to play the role of the computer system. Here's how it works:

• The script should include the proposed introduction, prompts, list of global commands, and all planned self-revealing help. Consider Table 1 as an example of a script appropriate for “Wizard of Oz” testing:

  Table 1. Sample script for “Wizard of Oz” testing

  Title	Message types	Prompts and responses	System actions
  Greeting	Intro message	Welcome to Phone Pay! You can say Repeat or Help at any time.	Go to Get Account Number.
  Get Account Number	Prompt	Account number?
  	Help1	Your account number is on the upper-right portion of your bill. Speak only the numbers on the left side of the dash. You can ignore leading zeros.
  	Help2	At any time, you can say Help, Repeat, Go Back, Main Menu, Exit, or Transfer to Agent. To continue, say or enter your account number.
  	Caller response	<Says or enters numbers>	If input spoken, go to Confirm Account Number. If entered via DTMF, go to Get PIN Number.
  Confirm Account Number	Prompt	Was that <number>?
  	Help1	Please say Yes, No, or Repeat.
  	Help2	At any time, you can say Help, Repeat, Go Back, Main Menu, Exit, or Transfer to Agent. To continue, say Yes or No.
  	Caller response	Yes	Go to Get PIN Number.
  	Caller response	No	Go to Get Account Number.

• The two participants should be physically separated so that they cannot use visual cues to communicate; a partition will suffice, or you could use separate rooms and allow the people to communicate by telephone.
• The wizard must be very familiar with the script. The user should never see the script.
• The user telephones (or pretends to telephone) the wizard, who begins reading the script aloud. The user responds to the prompts, and the wizard continues the dialog based on the scripted response to the user's utterance.

“Wizard of Oz” testing helps you fix problems in the script and task flow before committing any of the design to code. However, it cannot detect other types of usability problems, such as recognition or audio quality problems; addressing problems linked to these types of errors requires a working prototype.