Added golines playground

cmds/golines/recovery_test.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestFormatterPanicRecovery(t *testing.T) {
+	// go/format accepts fragments, but dst v0.27.3 panics when golines
+	// attempts to decorate this function without a package declaration.
+	source := `func example() {
+ println("first argument", "second argument", "third argument", "fourth argument")
+}`
+	output, err := formatSource(source, 40)
+	if err == nil || !strings.Contains(err.Error(), "internal panic") {
+		t.Fatalf("expected recovered dependency panic, got output %q, error %v", output, err)
+	}
+	if output != nil {
+		t.Fatalf("unexpected output after panic: %q", output)
+	}
+	output, err = formatSource("package main\n"+source, 40)
+	if err != nil || !strings.Contains(string(output), "func example()") {
+		t.Fatalf("formatting after panic failed: output %q, error %v", output, err)
+	}
+}