From cfc76f269987851160ccc71a91178056f5df25ea Mon Sep 17 00:00:00 2001
From: Enes Uygur <enesuygurs@gmail.com>
Date: Fri, 23 Oct 2026 16:53:21 +0300
Subject: [PATCH] fix: clear prop for getter calls with a message in assert
 delta helpers

---
 lib/chai/interface/assert.js |  7 +++++++
 test/assert.js               | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/lib/chai/interface/assert.js b/lib/chai/interface/assert.js
index 4fd39807..fd448ecf 100644
--- a/lib/chai/interface/assert.js
+++ b/lib/chai/interface/assert.js
@@ -2614,6 +2614,7 @@ assert.changesBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2675,6 +2676,7 @@ assert.changesButNotBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2735,6 +2737,7 @@ assert.increasesBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2798,6 +2801,7 @@ assert.increasesButNotBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2858,6 +2862,7 @@ assert.decreasesBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2923,6 +2928,7 @@ assert.doesNotDecreaseBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
@@ -2956,6 +2962,7 @@ assert.decreasesButNotBy = function (fn, obj, prop, delta, msg) {
     let tmpMsg = delta;
     delta = prop;
     msg = tmpMsg;
+    prop = null;
   } else if (arguments.length === 3) {
     delta = prop;
     prop = null;
diff --git a/test/assert.js b/test/assert.js
index eb91911a..f9f43045 100644
--- a/test/assert.js
+++ b/test/assert.js
@@ -2460,6 +2460,8 @@ describe('assert', function () {
     assert.doesNotChange(smFn, getterFn, 'value');
     assert.changesButNotBy(fnDec, obj, 'value', 1);
     assert.changesButNotBy(fnDec, getterFn, 1);
+    assert.changesBy(fn, getterFn, 5, 'via getter function');
+    assert.changesButNotBy(fnDec, getterFn, 1, 'via getter function');
 
     assert.changes(bangFn, obj, 'str');
 
@@ -2496,6 +2498,10 @@ describe('assert', function () {
     err(function () {
       assert.changesButNotBy(fn, obj, 'value', 5, 'blah');
     }, "blah: expected .value to not change by 5");
+
+    err(function () {
+      assert.changesBy(smFn, function () { return 1 }, 1, 'blah');
+    }, "blah: expected 1 to change");
   });
 
   it('increase, decrease', function() {
@@ -2517,6 +2523,8 @@ describe('assert', function () {
     assert.decreasesBy(decFn, getterFn, 3);
     assert.decreasesButNotBy(decFn, obj, 'value', 10);
     assert.decreasesButNotBy(decFn, getterFn, 10);
+    assert.decreasesBy(decFn, getterFn, 3, 'via getter function');
+    assert.decreasesButNotBy(decFn, getterFn, 10, 'via getter function');
 
     assert.increases(incFn, obj, 'value');
     assert.increases(incFn, getterFn, 'increases via getter function');
@@ -2526,6 +2534,8 @@ describe('assert', function () {
     assert.increasesBy(incFn, getterFn, 2);
     assert.increasesButNotBy(incFn, obj, 'value', 1);
     assert.increasesButNotBy(incFn, getterFn, 1);
+    assert.increasesBy(incFn, getterFn, 2, 'via getter function');
+    assert.increasesButNotBy(incFn, getterFn, 1, 'via getter function');
 
     const zeroArr = [10];
     const zeroInc = function() { zeroArr[0] += 2 };