Systems Fail at Their Interfaces

Lab Brief #5

🎯 Your mission

Run the experiment. Find out what really happens.

⚡ The twist

Constraints make you more creative, not less.

What you'll learn

Components tested individually can all pass while the assembled system fails, because most failures happen where parts meet — a joint, a connector, a protocol, or a handover between two teams who each assumed the other had covered something. This is why engineers test the integrated system rather than only its parts, and why an interface should be written down and agreed before either side is built. The interface is the part nobody owns unless somebody is made to own it.

Key words

interface
The boundary where two components or two teams meet, and where most system failures originate.
integration testing
Testing the assembled system rather than its components individually, to catch interface failures.

Make a hypothesis first

Before you test: how many tries until it works?

Say your guess out loud — then find out if you were right.

Get ready

🧰 What you need

card tubes
sticky tape
marbles
stopwatch
specification sheet

Get ready

⚠️ Safety first

Marbles are a choking hazard — keep them away from young children and off the floor.

Step 1 of 4 · Read

Think about what you just learned: say what "interface" and "integration testing" mean in your own words before you start.

Step 2 of 4 · Do

In pairs, each build half of a marble run to a written interface specification without seeing the other half, then join them and test. Record every failure at the joint and rewrite the specification so the same failures could not recur.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 3

Most system failures originate:

How sure are you?😐 maybe

Question 2 of 3

Integration testing is needed because components that each pass alone may still:

How sure are you?😐 maybe

Question 3 of 3

An interface specification should be agreed:

How sure are you?😐 maybe

Mind = blown

🌉 The Eiffel Tower can grow 6 inches taller in summer because metal expands when hot.

Nice work!

You got 0 of 3 right.

All lessons

🎯

Next Smart Experiment

We'll pick an experiment that matches exactly how you're thinking right now.

✨ More to explore

🌍 Where you see this in real life: Your phone, your bike, your shoes — all designed with this idea.

🏆 Stretch challenge (try it this week): Build something — anything — out of stuff in your recycling bin.

👨‍👩‍👧 For the dinner table: “What's something around the house you'd redesign — and how?”

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Systems Fail at Their Interfaces

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Systems Fail at Their Interfaces

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