add a regression test based on #195

Author: gfx

Diff for: test/reuse-instances-with-extensions.test.ts

@@ -0,0 +1,41 @@
+// https://github.com/msgpack/msgpack-javascript/issues/195
+
+import { deepStrictEqual } from "assert";
+import { Encoder, Decoder, ExtensionCodec } from "../src/index";
+
+const MSGPACK_EXT_TYPE_BIGINT = 0;
+
+function registerCodecs(context: MsgPackContext) {
+  const { extensionCodec, encode, decode } = context;
+
+  extensionCodec.register({
+    type: MSGPACK_EXT_TYPE_BIGINT,
+    encode: (value) => (typeof value === "bigint" ? encode(value.toString()) : null),
+    decode: (data) => BigInt(decode(data) as string),
+  });
+}
+
+class MsgPackContext {
+  readonly encode: (value: unknown) => Uint8Array;
+  readonly decode: (buffer: BufferSource | ArrayLike<number>) => unknown;
+  readonly extensionCodec = new ExtensionCodec<MsgPackContext>();
+
+  constructor() {
+    const encoder = new Encoder<MsgPackContext>({ extensionCodec: this.extensionCodec, context: this });
+    const decoder = new Decoder<MsgPackContext>({ extensionCodec: this.extensionCodec, context: this });
+
+    this.encode = encoder.encode.bind(encoder);
+    this.decode = decoder.decode.bind(decoder);
+
+    registerCodecs(this);
+  }
+}
+
+describe("reuse instances with extensions", () => {
+  it("should encode and decode a bigint", () => {
+    const context = new MsgPackContext();
+    const buf = context.encode(BigInt(42));
+    const data = context.decode(buf);
+    deepStrictEqual(data, BigInt(42));
+  });
+});