test(autostart): keep the Linux tests away from an agent installed on the machine

internal/autostart/linux_test.go

@@ -8,8 +8,20 @@ import (
 	"testing"
 )
 
-func TestInstalledParsesEntries(t *testing.T) {
+// isolate keeps the tests away from the machine's own registration: a user config directory and package unit paths
+// in a temporary directory, so an agent installed on the machine running the tests does not count.
+func isolate(t *testing.T) {
+	t.Helper()
 	t.Setenv("XDG_CONFIG_HOME", t.TempDir())
+	system := t.TempDir()
+	units, enabled := systemUnits, globalEnabled
+	t.Cleanup(func() { systemUnits, globalEnabled = units, enabled })
+	systemUnits = []string{filepath.Join(system, "lib", UnitName), filepath.Join(system, "etc", UnitName)}
+	globalEnabled = filepath.Join(system, "etc", "default.target.wants", UnitName)
+}
+
+func TestInstalledParsesEntries(t *testing.T) {
+	isolate(t)
 	unit, desktop, err := paths()
 	if err != nil {
 		t.Fatal(err)
@@ -37,3 +49,27 @@ func TestInstalledParsesEntries(t *testing.T) {
 		t.Fatalf("systemd unit: %q, %v", got, ok)
 	}
 }
+
+// TestInstalledPackageUnit: the package's unit counts only once enabled for every user.
+func TestInstalledPackageUnit(t *testing.T) {
+	isolate(t)
+	exe := "/usr/bin/polinetwork-esign"
+	if err := os.MkdirAll(filepath.Dir(systemUnits[0]), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(systemUnits[0], []byte(SystemdUnit(exe)), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := Installed(); ok {
+		t.Fatal("installed while the package unit is not enabled")
+	}
+	if err := os.MkdirAll(filepath.Dir(globalEnabled), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink(systemUnits[0], globalEnabled); err != nil {
+		t.Fatal(err)
+	}
+	if got, ok := Installed(); !ok || got != exe {
+		t.Fatalf("package unit: %q, %v", got, ok)
+	}
+}