From 91577c8c098c88c4112ef7f7e9913712f81a1f8f Mon Sep 17 00:00:00 2001
From: Viljami Kuosmanen <viljami@viljami.io>
Date: Sat, 25 Jul 2026 16:06:52 +0200
Subject: [PATCH] Fix tests against axios 0.33
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axios 0.31–0.33 hardened `utils.merge` to build results with
`Object.create(null)`. `dispatchRequest` runs every config through that
merge, so `config.headers` reaches the adapter with a null prototype and
axios-mock-adapter's `config.headers.constructor.name === 'AxiosHeaders'`
check throws (same in axios-mock-adapter 2.1.0, so upgrading it does not
help). The same hardening makes `mergeConfig` produce null-prototype
`defaults.auth` / `defaults.proxy`, which `toStrictEqual` rejects on
prototype mismatch.

The library itself works fine under axios 0.33 — this was purely a test
tooling incompatibility, surfacing as 30 failures in the `0.*.*` CI
matrix entry.

- Add a jest setup that gives axios-mock-adapter a normal-prototype copy
  of the headers, only when they arrive with a null prototype, leaving
  AxiosHeaders detection untouched on axios 1.x and 0.25/0.30
- Relax the two prototype-sensitive `toStrictEqual` assertions to
  `toEqual`

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Co-authored-by: Claude <noreply@anthropic.com>
---
 jest.config.ts         |  1 +
 src/__tests__/setup.ts | 18 ++++++++++++++++++
 src/client.test.ts     |  4 ++--
 3 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 src/__tests__/setup.ts

diff --git a/jest.config.ts b/jest.config.ts
index 4c713a0..e4bdc06 100644
--- a/jest.config.ts
+++ b/jest.config.ts
@@ -3,6 +3,7 @@ import type { JestConfigWithTsJest } from 'ts-jest'
 const jestConfig: JestConfigWithTsJest = {
   testEnvironment: 'node',
   testMatch: ['**/?(*.)+(spec|test).ts?(x)'],
+  setupFilesAfterEnv: ['<rootDir>/src/__tests__/setup.ts'],
   transform: {
     '^.+\\.[tj]s?$': [
       'ts-jest',
diff --git a/src/__tests__/setup.ts b/src/__tests__/setup.ts
new file mode 100644
index 0000000..7410b3f
--- /dev/null
+++ b/src/__tests__/setup.ts
@@ -0,0 +1,18 @@
+import MockAdapter from 'axios-mock-adapter';
+import type { AxiosRequestConfig } from 'axios';
+
+/**
+ * axios >= 0.33 hardened its internal config/header merge to build null-prototype objects.
+ * axios-mock-adapter reads `config.headers.constructor.name` to detect AxiosHeaders, which
+ * throws on such objects. Hand the mock adapter a normal-prototype copy of the headers.
+ *
+ * @see https://github.com/ctimmerm/axios-mock-adapter/blob/master/src/handle_request.js
+ */
+const originalAdapter = MockAdapter.prototype.adapter;
+MockAdapter.prototype.adapter = function patchedAdapter(this: MockAdapter) {
+  const handleRequest = originalAdapter.call(this) as (config: AxiosRequestConfig) => Promise<unknown>;
+  return ((config: AxiosRequestConfig) =>
+    config.headers && Object.getPrototypeOf(config.headers) === null
+      ? handleRequest({ ...config, headers: { ...config.headers } })
+      : handleRequest(config)) as ReturnType<typeof originalAdapter>;
+};
diff --git a/src/client.test.ts b/src/client.test.ts
index ef6e32f..1de5be7 100644
--- a/src/client.test.ts
+++ b/src/client.test.ts
@@ -281,7 +281,7 @@ describe('OpenAPIClientAxios', () => {
       expect(d.timeout).toBe(1234);
       expect(d.withCredentials).toBe(true);
       expect(d.adapter).toBe(userAdapter);
-      expect(d.auth).toStrictEqual({
+      expect(d.auth).toEqual({
         username: 'fake',
         password: 'fakepassword'
       }),
@@ -296,7 +296,7 @@ describe('OpenAPIClientAxios', () => {
       expect(d.validateStatus).toBe(userValidateStatus);
       expect(d.maxRedirects).toBe(99);
       expect(d.socketPath).toBe('/fake/path/example');
-      expect(d.proxy).toStrictEqual({
+      expect(d.proxy).toEqual({
           host: '1.2.3.4',
           port: 9876,
           auth: {