Add snapshot tests to array.test.ts

mobxjs#2080

packages/mobx-state-tree/__tests__/core/array.test.ts

@@ -1,20 +1,20 @@
 import {
-    unprotect,
-    onSnapshot,
-    onPatch,
-    clone,
-    isAlive,
+    IJsonPatch,
     applyPatch,
-    getPath,
     applySnapshot,
+    cast,
+    clone,
+    detach,
+    getPath,
     getSnapshot,
-    types,
-    IJsonPatch,
+    isAlive,
+    onPatch,
+    onSnapshot,
     setLivelinessChecking,
-    detach,
-    cast
+    types,
+    unprotect
 } from "../../src"
-import { observable, autorun, configure } from "mobx"
+import { autorun, configure, observable } from "mobx"
 
 const createTestFactories = () => {
     const ItemFactory = types.optional(
@@ -55,6 +55,63 @@ test("it should emit snapshots", () => {
     doc.push(ItemFactory.create())
     expect(snapshots).toEqual([[{ to: "world" }]])
 })
+test("it should not emit snapshot on idempotent assignment to array of numbers", () => {
+    const store = types
+        .model({
+            todos: types.array(types.number)
+        })
+        .create({
+            todos: [1, 2, 3, 4]
+        })
+    unprotect(store)
+    let snapshots = []
+
+    onSnapshot(store, (snapshot) => snapshots.push(snapshot))
+
+    expect(snapshots.length).toEqual(0)
+
+    store.todos[0] = 1
+    expect(snapshots.length).toEqual(0)
+
+    store.todos.replace([1, 2, 3, 4])
+    expect(snapshots.length).toEqual(0)
+
+    store.todos[0] = 2
+    expect(snapshots.length).toEqual(1)
+})
+
+test("it should emit snapshot on idempotent assignment of objects", () => {
+    const Task = types.model("Task", {
+        x: types.string
+    })
+    const a = Task.create({ x: "a" }),
+        b = Task.create({ x: "b" }),
+        c = Task.create({ x: "c" }),
+        d = Task.create({ x: "d" })
+    const store = types
+        .model({
+            todos: types.array(Task)
+        })
+        .create({
+            todos: [a, b, c, d]
+        })
+    unprotect(store)
+    let snapshots = []
+
+    onSnapshot(store, (snapshot) => snapshots.push(snapshot))
+
+    expect(snapshots.length).toEqual(0)
+
+    store.todos[0].x = "a"
+    expect(snapshots.length).toEqual(0)
+
+    store.todos[0] = { x: "a" }
+    expect(snapshots.length).toEqual(1)
+
+    store.todos.replace([a, b, c, d])
+    expect(snapshots.length).toEqual(2)
+})
+
 test("it should apply snapshots", () => {
     const { Factory, ItemFactory } = createTestFactories()
     const doc = Factory.create()