add unit tests

Author: liustve

aws-distro-opentelemetry-node-autoinstrumentation/test/patches/instrumentation-patch.test.ts

@@ -543,26 +543,40 @@ describe('InstrumentationPatchTest', () => {
       const send = extractAwsSdkInstrumentation(PATCHED_INSTRUMENTATIONS)
         ['_getV3SmithyClientSendPatch']((...args: unknown[]) => Promise.resolve())
         .bind({ middlewareStack: mockedMiddlewareStack });
+
       sinon
         .stub(AWSXRayPropagator.prototype, 'inject')
-        .callsFake((context: OtelContext, carrier: unknown, setter: TextMapSetter) => {
-          (carrier as any)['isCarrierModified'] = 'carrierIsModified';
+        .callsFake((context: OtelContext, carrier: any, setter: TextMapSetter) => {
+          carrier['isCarrierModified'] = 'carrierIsModified';
         });
 
       // eslint-disable-next-line @typescript-eslint/ban-ts-comment
       // @ts-ignore
       await send({}, null);
 
-      const middlewareArgs: any = {
+      // Test case 1: With existing header
+      const existingHeader = 'test-trace-header';
+      const middlewareArgsWithHeader: any = {
+        request: {
+          headers: { [AWSXRAY_TRACE_ID_HEADER]: existingHeader },
+        },
+      };
+      await mockedMiddlewareStackInternal[0][0]((arg: any) => Promise.resolve(), null)(middlewareArgsWithHeader);
+      expect(middlewareArgsWithHeader.request.headers['isCarrierModified']).toEqual('carrierIsModified');
+      expect(middlewareArgsWithHeader.request.headers['X-Amzn-Trace-Id']).toEqual(existingHeader);
+
+      // Test case 2: Without existing header
+      const middlewareArgsNoHeader: any = {
         request: {
           headers: {},
         },
       };
-      await mockedMiddlewareStackInternal[0][0]((arg: any) => Promise.resolve(), null)(middlewareArgs);
+      await mockedMiddlewareStackInternal[0][0]((arg: any) => Promise.resolve(), null)(middlewareArgsNoHeader);
+      expect(middlewareArgsNoHeader.request.headers['isCarrierModified']).toEqual('carrierIsModified');
+      expect(middlewareArgsNoHeader.request.headers).not.toContain(AWSXRAY_TRACE_ID_HEADER);
 
-      sinon.restore();
-      expect(middlewareArgs.request.headers['isCarrierModified']).toEqual('carrierIsModified');
       expect(mockedMiddlewareStackInternal[0][1].name).toEqual('_adotInjectXrayContextMiddleware');
+      sinon.restore();
     });
 
     it('injects trace context header into request via propagator', async () => {