Add extension normalization command

tests/integration/extension_validation_test.go

@@ -0,0 +1,42 @@
+package integration
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	renamercmd "github.com/rogeecn/renamer/cmd"
+)
+
+func TestExtensionCommandBlocksConflicts(t *testing.T) {
+	t.Parallel()
+
+	tmp := t.TempDir()
+	createFile(t, filepath.Join(tmp, "doc.jpeg"))
+	createFile(t, filepath.Join(tmp, "doc.jpg"))
+
+	var out bytes.Buffer
+	cmd := renamercmd.NewRootCommand()
+	cmd.SetOut(&out)
+	cmd.SetErr(&out)
+	cmd.SetArgs([]string{"extension", ".jpeg", ".jpg", ".jpg", "--yes", "--path", tmp})
+
+	err := cmd.Execute()
+	if err == nil {
+		t.Fatalf("expected conflict to produce an error")
+	}
+
+	if !strings.Contains(out.String(), "existing") && !strings.Contains(out.String(), "conflict") {
+		t.Fatalf("expected conflict messaging in output, got: %s", out.String())
+	}
+
+	// Ensure files unchanged after failed apply.
+	if _, err := os.Stat(filepath.Join(tmp, "doc.jpeg")); err != nil {
+		t.Fatalf("expected doc.jpeg to remain: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(tmp, "doc.jpg")); err != nil {
+		t.Fatalf("expected doc.jpg to remain: %v", err)
+	}
+}