Add test for updateBaseBranch method

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/test/github/pullRequestModel.test.ts

@@ -148,4 +148,14 @@ describe('PullRequestModel', function () {
 			assert.strictEqual(onDidChangeReviewThreads.getCall(0).args[0]['removed'].length, 0);
 		});
 	});
+
+	describe('updateBaseBranch', function () {
+		it('should have updateBaseBranch method', function () {
+			const pr = new PullRequestBuilder().build();
+			const model = new PullRequestModel(credentials, telemetry, repo, remote, convertRESTPullRequestToRawPullRequest(pr, repo));
+
+			// Verify the method exists
+			assert.strictEqual(typeof model.updateBaseBranch, 'function');
+		});
+	});
 });