bun test: drain the event loop for script files with no test() registrations

src/jsc/VirtualMachine.rs

@@ -1059,6 +1059,22 @@ impl VirtualMachine {
             || !el.next_immediate_tasks.is_empty()
     }
 
+    /// Count of ref'd handles and outstanding tasks keeping the loop alive.
+    /// Snapshotted by the test runner as a per-file drain baseline so prior
+    /// leaks (or a --parallel worker's IPC pipe) are not waited on.
+    pub fn active_keepalive_count(&self) -> usize {
+        let el = self.event_loop_shared();
+        let active = self
+            .platform_loop_opt()
+            .map(|h| h.active_count() as usize)
+            .unwrap_or(0);
+        let concurrent = el
+            .concurrent_ref
+            .load(core::sync::atomic::Ordering::SeqCst)
+            .max(0) as usize;
+        active + self.active_tasks + concurrent
+    }
+
     pub fn wakeup(&mut self) {
         self.event_loop_mut().wakeup();
     }
@@ -4592,6 +4608,7 @@ impl VirtualMachine {
     pub fn reload_entry_point_for_test_runner(
         &mut self,
         entry_path: &[u8],
+        after_preloads: impl FnOnce(&Self),
     ) -> crate::CrateResult<*mut JSInternalPromise> {
         self.has_loaded = false;
         self.set_main(entry_path);
@@ -4618,6 +4635,8 @@ impl VirtualMachine {
             }
         }
 
+        after_preloads(self);
+
         // Note: reshaped for borrowck.
         let global = self.global;
         let main_str = bun_core::String::from_bytes(self.main());
@@ -4648,11 +4667,14 @@ impl VirtualMachine {
     }
 
     /// Loads a test-file entry point and waits for the load promise to settle.
+    /// `after_preloads` runs between preload completion and entry-point
+    /// evaluation so the caller can observe preload-created handles.
     pub fn load_entry_point_for_test_runner(
         &mut self,
         entry_path: &[u8],
+        after_preloads: impl FnOnce(&Self),
     ) -> crate::CrateResult<*mut JSInternalPromise> {
-        let promise = self.reload_entry_point_for_test_runner(entry_path)?;
+        let promise = self.reload_entry_point_for_test_runner(entry_path, after_preloads)?;
 
         // pending_internal_promise can change if hot module reloading is enabled
         if self.is_watcher_enabled() {

src/libuv_sys/libuv.rs

@@ -507,6 +507,10 @@ impl Loop {
         unsafe { uv_loop_alive(self) != 0 }
     }
     #[inline]
+    pub fn active_count(&self) -> u32 {
+        self.active_handles
+    }
+    #[inline]
     pub fn tick(&mut self) {
         // SAFETY: self is a live loop.
         let _ = unsafe { uv_run(self, RunMode::Default) };

src/runtime/cli/test_command.rs

@@ -3142,7 +3142,12 @@ impl TestCommand {
 
             // need to wake up so autoTick() doesn't wait for 16-100ms after loading the entrypoint
             vm.wakeup();
-            let promise = vm.load_entry_point_for_test_runner(file_path)?;
+            // Record whether the loop was idle after preloads so the post-test
+            // drain (below) only runs when every ref'd handle is this file's.
+            let mut idle_after_preloads = false;
+            let promise = vm.load_entry_point_for_test_runner(file_path, |vm| {
+                idle_after_preloads = script_keepalive_count(vm) == 0;
+            })?;
             // Only count the file once, not once per repeat
             if repeat_index == 0 {
                 reporter.summary().files += 1;
@@ -3233,6 +3238,18 @@ impl TestCommand {
                     }
                 }
 
+                // A file with no test()/describe() is a plain script: drain the
+                // loop so late errors surface (like `bun <file>`). Gated on an
+                // idle loop after preloads so prior-file handles can't hang it.
+                if buntest.collection.root_scope.entries.is_empty() && idle_after_preloads {
+                    let drain_base = vm.unhandled_error_counter;
+                    while drain_base == vm.unhandled_error_counter && script_keepalive_count(vm) > 0
+                    {
+                        vm.event_loop_ref().tick();
+                        vm.event_loop_ref().auto_tick();
+                    }
+                }
+
                 let el = vm.event_loop();
                 // SAFETY: el is the VM-owned event loop; vm is passed back as *mut.
                 unsafe { (*el).tick_immediate_tasks(vm) };
@@ -3260,6 +3277,21 @@ impl TestCommand {
     }
 }
 
+/// Count of ref'd handles plus individual JS timers (timers share one loop
+/// ref, so `active_count()` alone misses additional timers). Zero means the
+/// file's own work is the only thing keeping the loop alive.
+fn script_keepalive_count(vm: &VirtualMachine) -> usize {
+    let state = crate::jsc_hooks::runtime_state();
+    let timers = if state.is_null() {
+        0
+    } else {
+        // SAFETY: `runtime_state()` returns the live per-thread `RuntimeState`;
+        // `active_timer_count` is plain data, read on the owning JS thread.
+        unsafe { (*state).timer.active_timer_count.max(0) as usize }
+    };
+    vm.active_keepalive_count() + timers
+}
+
 pub(crate) fn handle_top_level_test_error_before_javascript_start(err: &crate::Error) -> ! {
     if cfg!(debug_assertions) {
         if !matches!(err, crate::Error::ModuleNotFound) {

src/uws_sys/Loop.rs

@@ -182,6 +182,11 @@ impl PosixLoop {
         self.active > 0
     }
 
+    #[inline]
+    pub fn active_count(&self) -> u32 {
+        self.active
+    }
+
     // This exists as a method so that we can stick a debugger in here
     pub fn add_active(&mut self, value: u32) {
         bun_core::scoped_log!(

test/cli/test/bun-test.test.ts

@@ -1458,6 +1458,176 @@ describe("bun test", () => {
   });
 });
 
+// https://github.com/oven-sh/bun/issues/34859
+describe.concurrent("script files with no test() registrations", () => {
+  test("fails on a delayed unhandled rejection from an async IIFE", async () => {
+    using dir = tempDir("script-delayed-rejection", {
+      "delayed.test.js": `
+        'use strict';
+        (async () => {
+          await new Promise(r => setTimeout(r, 20));
+          throw new Error("delayed rejection should fail the test run");
+        })();
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./delayed.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("delayed rejection should fail the test run");
+    expect(stderr).toContain("Unhandled error between tests");
+    expect(stderr).toContain("1 error");
+    expect(exitCode).toBe(1);
+  });
+
+  test("fails on a delayed uncaught exception from a timer", async () => {
+    using dir = tempDir("script-delayed-throw", {
+      "delayed.test.js": `setTimeout(() => { throw new Error("boom from timer"); }, 20);`,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./delayed.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("boom from timer");
+    expect(stderr).toContain("Unhandled error between tests");
+    expect(exitCode).toBe(1);
+  });
+
+  test("waits for ref'd async work to complete", async () => {
+    using dir = tempDir("script-drain", {
+      "drain.test.js": `
+        const assert = require("assert");
+        (async () => {
+          await new Promise(r => setTimeout(r, 20));
+          assert.strictEqual(1, 1);
+          console.log("reached end of async iife");
+        })();
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./drain.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stdout).toContain("reached end of async iife");
+    expect(stderr).toContain("0 fail");
+    expect(exitCode).toBe(0);
+  });
+
+  test("drains per file so a later script file's delayed rejection is caught", async () => {
+    using dir = tempDir("script-two-files", {
+      "a.test.js": `
+        (async () => {
+          await Promise.resolve();
+          throw new Error("file A microtask error");
+        })();
+      `,
+      "b.test.js": `
+        (async () => {
+          await new Promise(r => setTimeout(r, 20));
+          throw new Error("file B delayed error");
+        })();
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./a.test.js", "./b.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("file A microtask error");
+    expect(stderr).toContain("file B delayed error");
+    expect(exitCode).toBe(1);
+  });
+
+  test("does not drain when the file registered a test()", async () => {
+    // Files that use bun:test keep today's behavior: the runner does not
+    // block on leaked handles after the last test finishes.
+    using dir = tempDir("registered-test-no-drain", {
+      "with.test.js": `
+        const { test } = require("bun:test");
+        setInterval(() => {}, 60_000);
+        test("noop", () => {});
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./with.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("1 pass");
+    expect(exitCode).toBe(0);
+  });
+
+  test("does not drain when a prior file left a ref'd handle", async () => {
+    // a leaks an interval. b's drain is skipped because the loop was not
+    // idle after preloads (it can't tell a's handle from its own). The run
+    // must not hang; b's own delayed error goes unreported, same as before.
+    using dir = tempDir("prior-file-leak", {
+      "a.test.js": `
+        const { test } = require("bun:test");
+        setInterval(() => {}, 60_000);
+        test("noop", () => {});
+      `,
+      "b.test.js": `
+        (async () => {
+          await new Promise(r => setTimeout(r, 20));
+          throw new Error("file B delayed error");
+        })();
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "./a.test.js", "./b.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("1 pass");
+    expect(stderr).toContain("0 fail");
+    expect(exitCode).toBe(0);
+  });
+
+  test("does not drain when a preload left a ref'd handle", async () => {
+    using dir = tempDir("preload-leak", {
+      "setup.js": `setInterval(() => {}, 60_000);`,
+      "a.test.js": `
+        (async () => {
+          await new Promise(r => setTimeout(r, 20));
+          throw new Error("should not hang");
+        })();
+      `,
+    });
+    await using proc = Bun.spawn({
+      cmd: [bunExe(), "test", "--preload", "./setup.js", "./a.test.js"],
+      env: bunEnv,
+      cwd: String(dir),
+      stdout: "pipe",
+      stderr: "pipe",
+    });
+    const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+    expect(stderr).toContain("0 fail");
+    expect(exitCode).toBe(0);
+  });
+});
+
 function createTest(input?: string | (string | { filename: string; contents: string })[], filename?: string): string {
   const cwd = tmpdirSync();
   const inputs = Array.isArray(input) ? input : [input ?? ""];