test: add test for vuejs#6018

Author: johnsoncodehk

packages/reactivity/__tests__/reactiveArray.spec.ts

@@ -113,6 +113,25 @@ describe('reactivity/reactive/Array', () => {
     expect(fn).toHaveBeenCalledTimes(2)
   })
 
+  //#6018
+  test('edge case: avoid trigger effect in deleteProperty when array length-decrease mutation methods called', () => {
+    const arr = ref([1])
+    const fn1 = vi.fn()
+    const fn2 = vi.fn()
+    effect(() => {
+      fn1()
+      if (arr.value.length > 0) {
+        arr.value.slice()
+        fn2()
+      }
+    })
+    expect(fn1).toHaveBeenCalledTimes(1)
+    expect(fn2).toHaveBeenCalledTimes(1)
+    arr.value.splice(0)
+    expect(fn1).toHaveBeenCalledTimes(2)
+    expect(fn2).toHaveBeenCalledTimes(1)
+  })
+
   test('add existing index on Array should not trigger length dependency', () => {
     const array = new Array(3)
     const observed = reactive(array)