fix(Basic LLM Chain Node): Use correct mimetype for binary data (#12978)

packages/@n8n/nodes-langchain/nodes/chains/ChainLLM/test/utils.test.ts

@@ -0,0 +1,23 @@
+import { mock } from 'jest-mock-extended';
+import type { IBinaryData } from 'n8n-workflow';
+
+import { dataUriFromImageData, UnsupportedMimeTypeError } from '../utils';
+
+describe('dataUriFromImageData', () => {
+	it('should not throw an error on images', async () => {
+		const mockBuffer = Buffer.from('Test data');
+		const mockBinaryData = mock<IBinaryData>({ mimeType: 'image/jpeg' });
+
+		const dataUri = dataUriFromImageData(mockBinaryData, mockBuffer);
+		expect(dataUri).toBe('data:image/jpeg;base64,VGVzdCBkYXRh');
+	});
+
+	it('should throw an UnsupportetMimeTypeError on non-images', async () => {
+		const mockBuffer = Buffer.from('Test data');
+		const mockBinaryData = mock<IBinaryData>({ mimeType: 'text/plain' });
+
+		expect(() => {
+			dataUriFromImageData(mockBinaryData, mockBuffer);
+		}).toThrow(UnsupportedMimeTypeError);
+	});
+});