Usability Testing

Testing with real people is how you find out if the design works — not by looking at it, but by watching someone use it.

When to Use

• After design-builder produces a working prototype
• Before declaring a design complete
• When the design-critic flags persona coverage gaps
• When assumptions about user behaviour need evidence

Process

Step 1: Define What You're Testing

Write 3-5 task scenarios that map to the core jobs in the brief. Each task:

• Starts with a realistic trigger — "You just bought a new plant and want to add it to the app"
• Has a clear success condition — "The plant appears in your list with a watering schedule"
• Does not tell the user how — never say "tap the + button"

Step 2: Select Participants

Recruit 5-8 participants. At minimum include:

• 1 person who uses a screen reader
• 1 person over 60
• 1 person who is not a native speaker of the interface language
• 1 person with low tech confidence

Reference inclusive-personas for the ability spectrum.

Step 3: Choose Method

Method	When to use	Minimum participants
Moderated think-aloud	New flows, complex interactions	5
Unmoderated remote	Simple tasks, large sample	8-12
Guerrilla (hallway)	POC validation, time-constrained	3-5
Accessibility audit with AT users	After build, before ship	2-3

Step 4: Write the Test Script

1. Welcome — explain what you're testing (the design, not them)
2. Background — 2-3 questions about their relationship to the problem
3. Tasks — present each scenario one at a time, observe silently
4. Debrief — "What was hardest?" "What would you change?"

Never help during a task. Silence is data.

Step 5: Analyse Findings

Classify outcomes per task:

• Completed easily — no hesitation, no errors
• Completed with difficulty — hesitation or errors but recovered
• Failed — could not complete
• Completed wrong — thought they succeeded but didn't

Severity: Critical (blocks 2+ participants), Major (significant difficulty), Minor (noticed but not impeding).

Step 6: Turn Findings Into Actions

Every finding becomes a design action: "[Severity] [What happened] → [Design action] → [Which agent handles it]"

What You Deliver

• Task success rates table
• Ranked findings by severity
• Design actions with agent assignments
• Recommendation: iterate / ship / rethink

Integration

• Informed by: inclusive-personas, design-discovery
• Feeds into: design-lead, design-builder, design-strategist