fix(test): run the hub fixture on Windows

- replace the POSIX shell fixture with a compiled Go helper named hub or hub.exe
- prepend the helper directory to PATH in TestMain so tests cannot invoke an installed hub binary
- add PowerShell build, install, and Windows path examples to the README
- ignore the generated stack-sync.exe binary

main_test.go

@@ -2,14 +2,63 @@ package main
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
+	"strings"
 	"testing"
 	"time"
 )
 
+func TestMain(m *testing.M) {
+	if os.Getenv("STACK_SYNC_TEST_HELPER") == "hub" {
+		marker := os.Getenv("STACK_SYNC_TEST_MARKER")
+		if err := os.WriteFile(marker, []byte(strings.Join(os.Args[1:], " ")), 0o644); err != nil {
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+		os.Exit(0)
+	}
+	os.Exit(m.Run())
+}
+
+func installFakeHub(t *testing.T, dir string) string {
+	t.Helper()
+	source, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+	name := "hub"
+	if runtime.GOOS == "windows" {
+		name += ".exe"
+	}
+	destination := filepath.Join(dir, name)
+	if err := os.Link(source, destination); err == nil {
+		return destination
+	}
+
+	input, err := os.Open(source)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer input.Close()
+	output, err := os.OpenFile(destination, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o755)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := io.Copy(output, input); err != nil {
+		_ = output.Close()
+		t.Fatal(err)
+	}
+	if err := output.Close(); err != nil {
+		t.Fatal(err)
+	}
+	return destination
+}
+
 func git(t *testing.T, dir string, args ...string) {
 	t.Helper()
 	cmd := exec.Command("git", append([]string{"-C", dir}, args...)...)
@@ -128,11 +177,9 @@ func TestSyncRechecksAndSkipsNewlyDirtyRepository(t *testing.T) {
 		t.Fatal(err)
 	}
 	marker := filepath.Join(root, "hub-was-called")
-	script := "#!/bin/sh\ntouch \"$STACK_SYNC_TEST_MARKER\"\n"
-	if err := os.WriteFile(filepath.Join(bin, "hub"), []byte(script), 0o755); err != nil {
-		t.Fatal(err)
-	}
+	installFakeHub(t, bin)
 	t.Setenv("PATH", bin+string(os.PathListSeparator)+os.Getenv("PATH"))
+	t.Setenv("STACK_SYNC_TEST_HELPER", "hub")
 	t.Setenv("STACK_SYNC_TEST_MARKER", marker)
 
 	results := syncAll(root, []repo{planned}, 1, time.Minute, io.Discard, true)
@@ -155,11 +202,9 @@ func TestSyncInvokesHubForCleanRepository(t *testing.T) {
 		t.Fatal(err)
 	}
 	marker := filepath.Join(root, "hub-was-called")
-	script := "#!/bin/sh\nprintf '%s' \"$*\" > \"$STACK_SYNC_TEST_MARKER\"\n"
-	if err := os.WriteFile(filepath.Join(bin, "hub"), []byte(script), 0o755); err != nil {
-		t.Fatal(err)
-	}
+	installFakeHub(t, bin)
 	t.Setenv("PATH", bin+string(os.PathListSeparator)+os.Getenv("PATH"))
+	t.Setenv("STACK_SYNC_TEST_HELPER", "hub")
 	t.Setenv("STACK_SYNC_TEST_MARKER", marker)
 
 	results := syncAll(root, []repo{planned}, 1, time.Minute, io.Discard, true)