Model based testing example

example/model-based-testing/MusicPlayer.ts

@@ -0,0 +1,47 @@
+/**
+ * Basic state machine
+ * Example of how fast-check can be derived for model based testing
+ */
+export class MusicPlayer {
+  private tracks: string[];
+  private isPlaying: boolean;
+  private playingId: number;
+
+  constructor(tracks: string[]) {
+    this.tracks = [...tracks];
+    this.isPlaying = false;
+    this.playingId = 0;
+  }
+
+  playing(): boolean {
+    return this.isPlaying;
+  }
+
+  currentTrackName(): string | null {
+    return this.playingId != null && this.playingId < this.tracks.length ? this.tracks[this.playingId] : null;
+  }
+
+  play(): void {
+    this.isPlaying = true;
+  }
+  pause(): void {
+    this.isPlaying = false;
+  }
+
+  addTrack(trackName: string, position: number): void {
+    this.tracks = [...this.tracks.slice(0, position), trackName, ...this.tracks.slice(position)];
+    if (this.playingId >= position) {
+      // comment this block to check bug detection
+      ++this.playingId;
+    }
+  }
+
+  next(): void {
+    if (++this.playingId === this.tracks.length) {
+      this.playingId = 0;
+    }
+  }
+  jump(position: number): void {
+    this.playingId = position;
+  }
+}

example/model-based-testing/helpers/Command.ts

@@ -0,0 +1,12 @@
+export interface Command<Model, Real> {
+  // Check if the model is in the right state to apply the command
+  // WARNING: does not change the model
+  checkPreconditions(m: Model): void;
+
+  // Apply the command on the model
+  apply(m: Model): void;
+
+  // Receive the non-updated model and the real or system under test
+  // Performs the checks post-execution - Throw in case of invalid state
+  run(m: Model, r: Real): void;
+}

example/model-based-testing/helpers/CommandExecutor.ts

@@ -0,0 +1,12 @@
+import { Command } from './Command';
+
+type Setup<Model, Real> = () => { model: Model; real: Real };
+export const CommandExecutor = <Model, Real>(s: Setup<Model, Real>, cmds: Command<Model, Real>[]): void => {
+  const { model, real } = s();
+  for (const c of cmds) {
+    if (c.checkPreconditions(model)) {
+      c.run(model, real);
+      c.apply(model);
+    }
+  }
+};

example/model-based-testing/test.ts

@@ -0,0 +1,108 @@
+import * as assert from 'assert';
+import * as fc from 'fast-check';
+import { Command } from './helpers/Command';
+import { CommandExecutor } from './helpers/CommandExecutor';
+
+import { MusicPlayer } from './MusicPlayer';
+
+class MusicPlayerModel {
+  isPlaying: boolean = false;
+  numTracks: number = 0;
+  tracksAlreadySeen: { [Key: string]: boolean } = {}; // our model forbid to append twice the same track
+}
+type MusicPlayerCommand = Command<MusicPlayerModel, MusicPlayer>;
+
+class PlayCommand implements MusicPlayerCommand {
+  checkPreconditions(m: MusicPlayerModel) {
+    return true;
+  }
+  apply(m: MusicPlayerModel) {
+    m.isPlaying = true;
+  }
+  run(m: MusicPlayerModel, p: MusicPlayer) {
+    p.play();
+    assert.ok(p.playing());
+  }
+  toString() {
+    return 'Play';
+  }
+}
+class PauseCommand implements MusicPlayerCommand {
+  checkPreconditions(m: MusicPlayerModel) {
+    return true;
+  }
+  apply(m: MusicPlayerModel) {
+    m.isPlaying = false;
+  }
+  run(m: MusicPlayerModel, p: MusicPlayer) {
+    p.pause();
+    assert.ok(!p.playing());
+  }
+  toString() {
+    return 'Pause';
+  }
+}
+class NextCommand implements MusicPlayerCommand {
+  checkPreconditions(m: MusicPlayerModel) {
+    return true;
+  }
+  apply(m: MusicPlayerModel) {
+    /**/
+  }
+  run(m: MusicPlayerModel, p: MusicPlayer) {
+    const trackBefore = p.currentTrackName();
+    p.next();
+    assert.equal(p.playing(), m.isPlaying);
+    if (m.numTracks === 1) {
+      assert.equal(p.currentTrackName(), trackBefore);
+    } else {
+      assert.notEqual(p.currentTrackName(), trackBefore);
+    }
+  }
+  toString() {
+    return 'Next';
+  }
+}
+class AddTrackCommand implements MusicPlayerCommand {
+  constructor(readonly position: number, readonly trackName: string) {}
+  checkPreconditions(m: MusicPlayerModel) {
+    return !m.tracksAlreadySeen[this.trackName];
+  }
+  apply(m: MusicPlayerModel) {
+    ++m.numTracks;
+    m.tracksAlreadySeen[this.trackName] = true;
+  }
+  run(m: MusicPlayerModel, p: MusicPlayer) {
+    const trackBefore = p.currentTrackName();
+    p.addTrack(this.trackName, this.position % (m.numTracks + 1)); // old model
+    assert.equal(p.playing(), m.isPlaying);
+    assert.equal(p.currentTrackName(), trackBefore);
+  }
+  toString() {
+    return `AddTrack(${this.position}, ${this.trackName})`;
+  }
+}
+
+describe('MusicPlayer', () => {
+  const TrackNameArb = fc.hexaString(1, 10);
+  const CommandsArb: fc.Arbitrary<MusicPlayerCommand[]> = fc.array(
+    fc.oneof(
+      fc.constant(new PlayCommand()),
+      fc.constant(new PauseCommand()),
+      fc.constant(new NextCommand()),
+      fc.record({ position: fc.nat(), trackName: TrackNameArb }).map(d => new AddTrackCommand(d.position, d.trackName))
+    )
+  );
+  it('should run fast-check on model based approach', () =>
+    fc.assert(
+      fc.property(fc.set(TrackNameArb, 1, 10), CommandsArb, (initialTracks, commands) => {
+        const real = new MusicPlayer(initialTracks);
+        const model = new MusicPlayerModel();
+        model.numTracks = initialTracks.length;
+        for (const t of initialTracks) {
+          model.tracksAlreadySeen[t] = true;
+        }
+        CommandExecutor(() => ({ model, real }), commands);
+      })
+    ));
+});

example/package.json

@@ -6,11 +6,12 @@
     "test:contains": "mocha contains/test.js",
     "test:knight": "mocha shadows-of-the-knight-codingame/test.js",
     "test:settings": "mocha optional-settings-combination/test.js",
-    "test": "npm run test:contains && npm run test:knight"
+    "test:model": "mocha --require ts-node/register model-based-testing/test.ts"
   },
   "devDependencies": {
     "fast-check": "file:..",
-    "mocha": "^5.0.0"
+    "mocha": "^5.0.0",
+    "ts-node": "^6.1.0"
   },
   "author": "Nicolas DUBIEN <github@dubien.org>",
   "license": "MIT"

example/run.sh

@@ -5,7 +5,7 @@ npm install
 
 status=0
 
-for testUnit in "contains:6:0" "knight:15:1" "settings:0:1"
+for testUnit in "contains:6:0" "knight:15:1" "settings:0:1" "model:1:0"
 do
     name=`echo "${testUnit}" | cut -d: -f1`
     success=`echo "${testUnit}" | cut -d: -f2`