From b09dc5d97df0dcfa10bc9c33de1940e4b334e09a Mon Sep 17 00:00:00 2001
From: Morgan Roderick <morgan@roderick.dk>
Date: Mon, 9 Jun 2025 20:06:12 +0200
Subject: [PATCH] chore!: remove assert.failException property

This was used for allowing customisation of the thrown error between
sandboxes and for customisation for integrations (most likely from the
days of BusterJS).

To my knowledge and what I've been able to find on GitHub, this has
never had any _production_ use by end users.

BREAKING CHANGE: this removes assert.failException from the API
---
 lib/sinon/assert.js  |  4 +---
 test/assert-test.js  | 22 ----------------------
 test/sandbox-test.js | 27 ---------------------------
 3 files changed, 1 insertion(+), 52 deletions(-)

diff --git a/lib/sinon/assert.js b/lib/sinon/assert.js
index 43a555804..374be4d8b 100644
--- a/lib/sinon/assert.js
+++ b/lib/sinon/assert.js
@@ -47,8 +47,6 @@ function createAssertObject(opts) {
     });
 
     const assert = {
-        failException: "AssertError",
-
         fail: function fail(message) {
             let msg = message;
             if (cleanedAssertOptions.shouldLimitAssertionLogs) {
@@ -58,7 +56,7 @@ function createAssertObject(opts) {
                 );
             }
             const error = new Error(msg);
-            error.name = this.failException || assert.failException;
+            error.name = "AssertError";
 
             throw error;
         },
diff --git a/test/assert-test.js b/test/assert-test.js
index 69b675017..101f439e1 100644
--- a/test/assert-test.js
+++ b/test/assert-test.js
@@ -57,14 +57,6 @@ describe("assert", function () {
     });
 
     describe(".fail", function () {
-        beforeEach(function () {
-            this.exceptionName = sinonAssert.failException;
-        });
-
-        afterEach(function () {
-            sinonAssert.failException = this.exceptionName;
-        });
-
         it("can be configured to limit the error message length", function () {
             const customAssert = sinonAssert.createAssertObject({
                 shouldLimitAssertionLogs: true,
@@ -87,17 +79,6 @@ describe("assert", function () {
                 },
             );
         });
-
-        it("throws configured exception type", function () {
-            sinonAssert.failException = "CustomError";
-
-            assert.exception(
-                function () {
-                    sinonAssert.fail("Some message");
-                },
-                { name: "CustomError" },
-            );
-        });
     });
 
     describe("with stubs", function () {
@@ -1352,7 +1333,6 @@ describe("assert", function () {
             sinonAssert.expose(test);
 
             assert.isFunction(test.fail);
-            assert.isString(test.failException);
             assert.isFunction(test.assertCalled);
             assert.isFunction(test.assertCalledOn);
             assert.isFunction(test.assertCalledWith);
@@ -1367,7 +1347,6 @@ describe("assert", function () {
                 includeFail: false,
             });
 
-            assert.equals(typeof failException, "undefined");
             /*eslint-disable no-undef*/
             assert.isFunction(assertCalled);
             assert.isFunction(assertCalledOn);
@@ -1401,7 +1380,6 @@ describe("assert", function () {
             sinonAssert.expose(test, { prefix: "" });
 
             assert.isFunction(test.fail);
-            assert.isString(test.failException);
             assert.isFunction(test.called);
             assert.isFunction(test.calledOn);
             assert.isFunction(test.calledWith);
diff --git a/test/sandbox-test.js b/test/sandbox-test.js
index 397b99718..4929c82c4 100644
--- a/test/sandbox-test.js
+++ b/test/sandbox-test.js
@@ -1965,31 +1965,4 @@ describe("Sandbox", function () {
             refute.equals(getter, spy.get);
         });
     });
-
-    describe(".assert", function () {
-        it("allows rebinding of .fail on a per-sandbox level", function () {
-            const sandboxA = createSandbox();
-            const sandboxB = createSandbox();
-
-            sandboxA.assert.failException = "CustomErrorA";
-            sandboxB.assert.failException = "CustomErrorB";
-
-            assert.exception(
-                function () {
-                    sandboxA.assert.fail("Some message");
-                },
-                { name: "CustomErrorA" },
-            );
-
-            assert.exception(
-                function () {
-                    sandboxB.assert.fail("Some message");
-                },
-                { name: "CustomErrorB" },
-            );
-
-            sandboxA.restore();
-            sandboxB.restore();
-        });
-    });
 });