add unit test for multipart error fix

Author: shemogumbe

packages/serialization/multipart/test/common/multipartSerializationWriter.ts

@@ -50,6 +50,21 @@ describe("MultipartSerializationWriter", () => {
 				.join(""),
 		);
 	});
+	it("serializes multipart body with correct CRLF delimiters", () => {
+		const multipartSerializationWriter = new MultipartSerializationWriter();
+		const mpBody = new MultipartBody();
+		mpBody.addOrReplacePart("testPart", "text/plain", "test content");
+		mpBody.requestAdapter = {
+		  getSerializationWriterFactory: () => new JsonSerializationWriterFactory(),
+		} as RequestAdapter;
+		
+		multipartSerializationWriter.writeObjectValue(undefined, mpBody, serializeMultipartBody);
+		const multipartContent = multipartSerializationWriter.getSerializedContent();
+		const result = new TextDecoder().decode(multipartContent);
+		
+		const expectedString = `--${mpBody.getBoundary()}\r\nContent-Type: text/plain\r\nContent-Disposition: form-data; name="testPart"\r\n\r\ntest content\r\n--${mpBody.getBoundary()}--\r\n`;
+		assert.equal(result, expectedString);
+	  });
 	it("writes a structured object", () => {
 		const testEntity = {} as TestEntity;
 		testEntity.id = "48d31887-5fad-4d73-a9f5-3c356e68a038";