Adds check to throw error if non-serializable state is used in a move

src/client/client.test.ts

@@ -471,19 +471,6 @@ describe('move dispatchers', () => {
     expect(store.getState().G).toMatchObject({ moved: '0' });
   });
 
-  test('with undefined playerID - multiplayer mode', () => {
-    const store = createStore(reducer, initialState);
-    const api = createMoveDispatchers(
-      game.moveNames,
-      store,
-      undefined,
-      null,
-      true
-    );
-    api.B();
-    expect(store.getState().G).toMatchObject({ moved: undefined });
-  });
-
   test('with null playerID - singleplayer mode', () => {
     const store = createStore(reducer, initialState);
     const api = createMoveDispatchers(game.moveNames, store, null);

src/core/game.test.ts

@@ -27,6 +27,15 @@ describe('basic', () => {
         C: {
           move: () => 'C',
         },
+        INVALID: () => {
+          class Foo {
+            a: number;
+            constructor(a: number) {
+              this.a = a;
+            }
+          }
+          return { a: new Foo(1) };
+        },
       },
 
       phases: {
@@ -40,7 +49,7 @@ describe('basic', () => {
   });
 
   test('sanity', () => {
-    expect(game.moveNames).toEqual(['A', 'B', 'C']);
+    expect(game.moveNames).toEqual(['A', 'B', 'C', 'INVALID']);
     expect(typeof game.processMove).toEqual('function');
   });
 
@@ -57,6 +66,16 @@ describe('basic', () => {
     expect(game.processMove(state, { type: 'A' })).toEqual('PA.A');
   });
 
+  test('invalid non-serializable state throws', () => {
+    const G = { test: true };
+    const ctx = { phase: '' };
+    const state = { G, ctx, plugins: {} };
+
+    expect(() => {
+      game.processMove(state, { type: 'INVALID' });
+    }).toThrow();
+  });
+
   test('long-form move syntax', () => {
     expect(
       game.processMove({ ctx: { phase: '' }, plugins: {} }, { type: 'C' })

src/core/game.ts

@@ -26,6 +26,21 @@ function IsProcessed(game: Game | ProcessedGame): game is ProcessedGame {
   return game.processMove !== undefined;
 }
 
+function checkSerializable(G: unknown) {
+  /* istanbul ignore if */
+  if (process.env.NODE_ENV !== 'test') {
+    // Only check on test environment.
+    return G;
+  }
+  const assert = require('assert');
+  assert.deepStrictEqual(
+    G,
+    JSON.parse(JSON.stringify(G)),
+    'Resulting state from move is not serialiazble.'
+  );
+  return G;
+}
+
 /**
  * Helper to generate the game move reducer. The returned
  * reducer has the following signature:
@@ -95,7 +110,7 @@ export function ProcessGameConfig(game: Game | ProcessedGame): ProcessedGame {
         if (action.args !== undefined) {
           args = args.concat(action.args);
         }
-        return fn(state.G, ctxWithAPI, ...args);
+        return checkSerializable(fn(state.G, ctxWithAPI, ...args));
       }
 
       logging.error(`invalid move object: ${action.type}`);