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 +1,32 @@
+// string-fragments.test.ts
+// SPDX-License-Identifier: MPL-2.0
+import { TokenizedStringFragments } from "../../lib/tokens/string-fragments";
+import { IFragmentConcatenator } from "../../lib/tokens/resolvable";
+
+// Helper function to create fragments with literals
+function createFragments(...literals: string[]): TokenizedStringFragments {
+  const fragments = new TokenizedStringFragments();
+  literals.forEach((literal) => fragments.addLiteral(literal));
+  return fragments;
+}
+
+describe("TokenizedStringFragments", () => {
+  test("concat method should merge fragments correctly", () => {
+    // Arrange: Create two instances with literals
+    const fragments1 = createFragments("Hello", ", ");
+    const fragments2 = createFragments("World", "!");
+
+    // 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 concatenatedResult = fragments1.join({
+      join(left: any, right: any): string {
+        return `${left}${right}`;
+      },
+    } as IFragmentConcatenator);
+
+    expect(concatenatedResult).toBe("Hello, World!"); // Verify merged content
+  });
+});