Add mock SwapDirectoriesAtomic implementation

This is only being used for unit tests on !linux platforms.

Author: tchap

pkg/operator/staticpod/file_utils_other.go

@@ -0,0 +1,41 @@
+//go:build !linux
+
+package staticpod
+
+import (
+	"fmt"
+	"math/rand/v2"
+	"os"
+	"path/filepath"
+)
+
+// SwapDirectoriesAtomic swaps two directories, but NOT atomically in this case.
+// Atomic implementation is only available for Linux.
+// This function is essentially a mock for tests, and it simply uses os.Rename.
+// In case there is any error, the swapping process is simply left in an inconsistent state.
+func SwapDirectoriesAtomic(dirA, dirB string) error {
+	// Still retain the constraints as in the Linux implementation.
+	if !filepath.IsAbs(dirA) {
+		return fmt.Errorf("not an absolute path: %q", dirA)
+	}
+	if !filepath.IsAbs(dirB) {
+		return fmt.Errorf("not an absolute path: %q", dirB)
+	}
+
+	// Rename dirA -> prevDirA.
+	prevDirA := fmt.Sprintf("%s-%d", dirA, rand.Int64())
+	if err := os.Rename(dirA, prevDirA); err != nil {
+		return fmt.Errorf("failed to rename %q to %q: %w", dirA, prevDirA, err)
+	}
+
+	// Rename dirB -> dirA.
+	if err := os.Rename(dirB, dirA); err != nil {
+		return fmt.Errorf("failed to rename %q to %q: %w", dirB, dirA, err)
+	}
+
+	// Rename prevDirA -> dirB.
+	if err := os.Rename(prevDirA, dirB); err != nil {
+		return fmt.Errorf("failed to rename %q to %q: %w", prevDirA, dirB, err)
+	}
+	return nil
+}