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22. Testing & screenshot tests 🔴

TTac has three kinds of tests, each at the cheapest level that can catch its bugs.

Kind Runs on Examples
Unit tests JVM, milliseconds rules, AI, reducers, protocol, geometry, Blocks, Word Hive
Screenshot tests (Roborazzi) JVM + Robolectric every image in this guide
Macrobenchmarks a real device cold start, frame timing, Baseline Profile generation 
./gradlew testDebugUnitTest      # unit + screenshot tests (capture off)
./gradlew recordRoborazziDebug   # re-record the guide's images
./gradlew verifyRoborazziDebug   # fail if rendering changed

Unit tests that play the game

Because rules are pure Kotlin, tests can play:

  • AiTest — Hard never loses 300 games against random play; Hard vs Hard always draws; the CPU blocks double threats on 5×5.
  • BlocksTest — a greedy bot evaluates every rotation and column and clears lines until it passes the Easy milestone. It found no bugs the day it was written — and it will catch the day a refactor breaks line clearing.
  • MatchTest — drives a whole LAN session with a fake host: illegal remote moves rejected, rematch handshake in both orders, AI replies on a test dispatcher.
  • StatsReducerTest / ArcadeAndLanTest — 21 straight wins produce exactly the right medals; three Blocks wins unlock the hive; the LAN board tracks streaks per alias.

Screenshot tests with Roborazzi

Roborazzi renders Compose on the JVM through Robolectric's native graphics and saves PNGs. DocShots (app/src/test/.../docs/DocShots.kt) captures the app's own composables — full screens, the real BoardCanvas, the backdrop, medals — never test-drawn diagrams.

The key trick is a paused clock, which makes animations deterministic:

rule.mainClock.autoAdvance = false
rule.setContent { TTacTheme(ThemeMode.DARK) { BoardCanvas(…) } }
rule.mainClock.advanceTimeBy(180)                  // exactly 180 ms into the animation
rule.onRoot().captureRoboImage("docs/images/mark-frame-180.png")
advanceTimeBy(80)
advanceTimeBy(80)
advanceTimeBy(180)
advanceTimeBy(180)
advanceTimeBy(300)
advanceTimeBy(300)
advanceTimeBy(700)
advanceTimeBy(700)

Same composable, same inputs, four moments — a frame-by-frame film strip of a real animation.

Infinite animations

With autoAdvance = true, a test waits for the UI to be idle — which never happens with an infinite backdrop. Pausing the clock and advancing it manually is what makes animated screens testable.

Going further

  • verifyRoborazziDebug in CI turns these images into visual regression tests: an accidental colour or layout change fails the build with a diff image.
  • Screens are rendered with a real AppViewModel on Robolectric's application, so they show live default state (the default profiles, a fresh hive) rather than mocked data.