Add a test with default only switch

test/Frontend/OpenQASM3/switch-default-only.qasm3

@@ -0,0 +1,32 @@
+OPENQASM 3.0;
+// RUN: qss-compiler -X=qasm --emit=ast-pretty %s | FileCheck %s --match-full-lines --check-prefix AST-PRETTY
+// RUN: qss-compiler -X=qasm --emit=mlir %s --enable-circuits-from-qasm=false| FileCheck %s --match-full-lines --check-prefixes MLIR
+// RUN: qss-compiler -X=qasm --emit=mlir %s --enable-circuits-from-qasm | FileCheck %s --match-full-lines --check-prefixes MLIR
+
+//
+// This code is part of Qiskit.
+//
+// (C) Copyright IBM 2023, 2024.
+//
+// This code is licensed under the Apache License, Version 2.0 with LLVM
+// Exceptions. You may obtain a copy of this license in the LICENSE.txt
+// file in the root directory of this source tree.
+//
+// Any modifications or derivative works of this code must retain this
+// copyright notice, and modified files need to carry a notice indicating
+// that they have been altered from the originals.
+
+int i = 15;
+qubit $0;
+// MLIR: quir.switch %{{.*}}{
+// MLIR-NEXT: }[]
+// AST-PRETTY: SwitchStatementNode(SwitchQuantity(name=i, type=ASTTypeIdentifier),
+switch (i) {
+    // AST-PRETTY:statements=[
+    // AST-PRETTY:],
+    // AST-PRETTY:default statement=[
+    // AST-PRETTY:])
+    default: {
+    }
+    break;
+}