[#667] sanity checks for Yjs caveats. In dev_mode, objects inserted into Yjs can't be manipulated.

tests/y-array.tests.js

@@ -4,6 +4,9 @@ import * as Y from '../src/index.js'
 import * as t from 'lib0/testing'
 import * as prng from 'lib0/prng'
 import * as math from 'lib0/math'
+import * as env from 'lib0/environment'
+
+const isDevMode = env.getVariable('node_env') === 'development'
 
 /**
  * @param {t.TestCase} tc
@@ -17,6 +20,28 @@ export const testBasicUpdate = tc => {
   t.compare(doc2.getArray('array').toArray(), ['hi'])
 }
 
+/**
+ * @param {t.TestCase} tc
+ */
+export const testFailsObjectManipulationInDevMode = tc => {
+  if (isDevMode) {
+    t.info('running in dev mode')
+    const doc = new Y.Doc()
+    const a = [1, 2, 3]
+    const b = { o: 1 }
+    doc.getArray('test').insert(0, [a])
+    doc.getMap('map').set('k', b)
+    t.fails(() => {
+      a[0] = 42
+    })
+    t.fails(() => {
+      b.o = 42
+    })
+  } else {
+    t.info('not in dev mode')
+  }
+}
+
 /**
  * @param {t.TestCase} tc
  */