misc/getfiles: add tests for getFile

This adds some tests for getFile, one of which would have caught
the recent recursion issue and other will hopefully catch future
regressions.

Part-of: https://gitlab.postmarketos.org/postmarketOS/postmarketos-mkinitfs/-/merge_requests/65

[ci:skip-build]: already built successfully in CI

internal/misc/getfiles_test.go

@@ -0,0 +1,149 @@
+// Copyright 2025 Clayton Craft <clayton@craftyguy.net>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package misc
+
+import (
+	"os"
+	"path/filepath"
+	"reflect"
+	"sort"
+	"testing"
+	"time"
+)
+
+func TestGetFile(t *testing.T) {
+	subtests := []struct {
+		name     string
+		setup    func(tmpDir string) (inputPath string, expectedFiles []string, err error)
+		required bool
+	}{
+		{
+			name: "symlink to directory - no infinite recursion",
+			setup: func(tmpDir string) (string, []string, error) {
+				// Create target directory with files
+				targetDir := filepath.Join(tmpDir, "target")
+				if err := os.MkdirAll(targetDir, 0755); err != nil {
+					return "", nil, err
+				}
+
+				testFile1 := filepath.Join(targetDir, "file1.txt")
+				testFile2 := filepath.Join(targetDir, "file2.txt")
+				if err := os.WriteFile(testFile1, []byte("content1"), 0644); err != nil {
+					return "", nil, err
+				}
+				if err := os.WriteFile(testFile2, []byte("content2"), 0644); err != nil {
+					return "", nil, err
+				}
+
+				// Create symlink pointing to target directory
+				symlinkPath := filepath.Join(tmpDir, "symlink")
+				if err := os.Symlink(targetDir, symlinkPath); err != nil {
+					return "", nil, err
+				}
+
+				expected := []string{symlinkPath, testFile1, testFile2}
+				return symlinkPath, expected, nil
+			},
+			required: true,
+		},
+		{
+			name: "symlink to file - returns both symlink and target",
+			setup: func(tmpDir string) (string, []string, error) {
+				// Create target file
+				targetFile := filepath.Join(tmpDir, "target.txt")
+				if err := os.WriteFile(targetFile, []byte("content"), 0644); err != nil {
+					return "", nil, err
+				}
+
+				// Create symlink pointing to target file
+				symlinkPath := filepath.Join(tmpDir, "symlink.txt")
+				if err := os.Symlink(targetFile, symlinkPath); err != nil {
+					return "", nil, err
+				}
+
+				expected := []string{symlinkPath, targetFile}
+				return symlinkPath, expected, nil
+			},
+			required: true,
+		},
+		{
+			name: "regular file",
+			setup: func(tmpDir string) (string, []string, error) {
+				regularFile := filepath.Join(tmpDir, "regular.txt")
+				if err := os.WriteFile(regularFile, []byte("content"), 0644); err != nil {
+					return "", nil, err
+				}
+
+				expected := []string{regularFile}
+				return regularFile, expected, nil
+			},
+			required: true,
+		},
+		{
+			name: "regular directory",
+			setup: func(tmpDir string) (string, []string, error) {
+				// Create directory with files
+				dirPath := filepath.Join(tmpDir, "testdir")
+				if err := os.MkdirAll(dirPath, 0755); err != nil {
+					return "", nil, err
+				}
+
+				file1 := filepath.Join(dirPath, "file1.txt")
+				file2 := filepath.Join(dirPath, "subdir", "file2.txt")
+
+				if err := os.WriteFile(file1, []byte("content1"), 0644); err != nil {
+					return "", nil, err
+				}
+				if err := os.MkdirAll(filepath.Dir(file2), 0755); err != nil {
+					return "", nil, err
+				}
+				if err := os.WriteFile(file2, []byte("content2"), 0644); err != nil {
+					return "", nil, err
+				}
+
+				expected := []string{file1, file2}
+				return dirPath, expected, nil
+			},
+			required: true,
+		},
+	}
+
+	for _, st := range subtests {
+		t.Run(st.name, func(t *testing.T) {
+			tmpDir := t.TempDir()
+
+			inputPath, expectedFiles, err := st.setup(tmpDir)
+			if err != nil {
+				t.Fatalf("setup failed: %v", err)
+			}
+
+			// Add timeout protection for infinite recursion test
+			done := make(chan struct{})
+			var files []string
+			var getFileErr error
+
+			go func() {
+				defer close(done)
+				files, getFileErr = getFile(inputPath, st.required)
+			}()
+
+			select {
+			case <-done:
+				if getFileErr != nil {
+					t.Fatalf("getFile failed: %v", getFileErr)
+				}
+			case <-time.After(5 * time.Second):
+				t.Fatal("getFile appears to be in infinite recursion (timeout)")
+			}
+
+			// Sort for comparison
+			sort.Strings(expectedFiles)
+			sort.Strings(files)
+
+			if !reflect.DeepEqual(expectedFiles, files) {
+				t.Fatalf("expected: %q, got: %q", expectedFiles, files)
+			}
+		})
+	}
+}