test: keep the suite runnable on Windows under Node 24+

tests/index.js

@@ -12,6 +12,11 @@ const assert = require("node:assert");
 
 const TEST_TIMEOUT = 60000;
 
+// see tests/win-exit-delay.cjs: without it every test crashes on exit under Node 24+ on Windows
+const NODE_ARGS = process.platform === 'win32'
+    ? `--require "${path.join(__dirname, 'win-exit-delay.cjs')}" `
+    : '';
+
 const testPath = path.join(__dirname, 'tests');
 
 let testCategories = fs.readdirSync(testPath).sort((a, b) => parseInt(a) - parseInt(b));
@@ -65,7 +70,7 @@ for (const testCategory of testCategories) {
                     };
 
                     let execTest = async (testPath) => {
-                        return (await exec(`node ${testPath}`, {maxBuffer: 1024 * 1024 * 100})).stdout
+                        return (await exec(`node ${NODE_ARGS}${testPath}`, {maxBuffer: 1024 * 1024 * 100})).stdout
                     }
 
                     try {

tests/win-exit-delay.cjs

@@ -0,0 +1,19 @@
+// Node 24 and later crash on Windows when process.exit() runs while undici still has
+// keep-alive sockets open: "Assertion failed: !(handle->flags & UV_HANDLE_CLOSING),
+// file src\win\async.c" (nodejs/node#56645). Every test here ends with process.exit()
+// right after fetching, so they hit it, and the crash also loses whatever stdout was
+// still buffered, which makes the captured output unreliable on top of the exit code.
+//
+// Letting the loop settle first avoids it. Preloaded by tests/index.js on win32 only,
+// so nothing changes on Linux or macOS.
+
+const EXIT_DELAY_MS = 100;
+
+const realExit = process.exit.bind(process);
+
+process.exit = (code) => {
+    if (code !== undefined) {
+        process.exitCode = code;
+    }
+    setTimeout(() => realExit(process.exitCode), EXIT_DELAY_MS);
+};