test: speed up (#1386)

Reduce redundant fixture setup, Git subprocesses, and large data copies while preserving test coverage.

Local macOS measurements against main:

| Measurement | Before | After |
| --- | ---: | ---: |
| Git package time, median of 3 alternating runs | 4.09 s | 3.48 s (-15%) |
| Allocations across 18 action-bundle cases | 489 MiB | 251 MiB (-49%) |
| Traced Git starts per checkout table run | 234 | 175 |

Reviewed-on: https://gitea.com/gitea/runner/pulls/1386
Reviewed-by: bircni <[email protected]>

internal/pkg/process/killer_windows_test.go

@@ -5,7 +5,6 @@ package process
 
 import (
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sys/windows"
@@ -25,6 +24,23 @@ func processAlive(pid int) bool {
 	return code == stillActive
 }
 
+func newProcessExitWaiter(t *testing.T, pids ...int) func() {
+	t.Helper()
+	handles := make([]windows.Handle, 0, len(pids))
+	for _, pid := range pids {
+		handle, err := windows.OpenProcess(windows.SYNCHRONIZE, false, uint32(pid))
+		require.NoError(t, err)
+		t.Cleanup(func() { require.NoError(t, windows.CloseHandle(handle)) })
+		handles = append(handles, handle)
+	}
+	return func() {
+		t.Helper()
+		result, err := windows.WaitForMultipleObjects(handles, true, 20000)
+		require.NoError(t, err)
+		require.EqualValues(t, windows.WAIT_OBJECT_0, result, "processes should exit: %v", pids)
+	}
+}
+
 func TestKillerKillsTree(t *testing.T) {
 	cmd, ready := newTestProcess(t, "parent", false)
 	require.NoError(t, cmd.Start())
@@ -39,9 +55,7 @@ func TestKillerKillsTree(t *testing.T) {
 	childPID := ready()
 	require.True(t, processAlive(childPID), "child process should start")
 
+	waitForExit := newProcessExitWaiter(t, cmd.Process.Pid, childPID)
 	require.NoError(t, killer.Kill())
-
-	require.Eventually(t, func() bool {
-		return !processAlive(cmd.Process.Pid) && !processAlive(childPID)
-	}, 20*time.Second, 200*time.Millisecond, "parent and child should both be terminated")
+	waitForExit()
 }