test(lib): add test for concat method in TokenizedStringFragments

Added a test case to verify that the `concat` method correctly merges fragments from another instance.

packages/cdktf/test/tokens/string-fragments.test.ts

@@ -0,0 +1,31 @@
+// Copyright (c) HashiCorp, Inc
+// SPDX-License-Identifier: MPL-2.0
+import { TokenizedStringFragments } from "../../lib/tokens/string-fragments";
+import { IFragmentConcatenator } from "../../lib/tokens/resolvable";
+
+describe("TokenizedStringFragments", () => {
+  test("concat method should merge fragments correctly", () => {
+    // Arrange: Create two instances with literals
+    const fragments1 = new TokenizedStringFragments();
+    fragments1.addLiteral("Hello");
+    fragments1.addLiteral(", ");
+
+    const fragments2 = new TokenizedStringFragments();
+    fragments2.addLiteral("World");
+    fragments2.addLiteral("!");
+
+    // Act: Concatenate fragments2 into fragments1
+    fragments1.concat(fragments2);
+
+    // Assert: Check the length and combined result
+    expect(fragments1.length).toBe(4); // Verify total number of fragments
+
+    const result = fragments1.join({
+      join(left: any, right: any): string {
+        return `${left}${right}`;
+      },
+    } as IFragmentConcatenator);
+
+    expect(result).toBe("Hello, World!"); // Verify merged content
+  });
+});